The federal government is hoping for speedy and painless delivery of its bill to change the gender rules for royal succession, but there are some complicating constitutional factors that could slow things down.

The legislation, expected to come in the first few weeks after MPs return from their winter break, is a rare and unprecedented example of a Canadian bill crafted in co-ordination with 15 other countries, which all need to do the same thing: take the first wee steps towards modernizing the monarchy.

But a nagging question lurks: Does changing the rules governing the monarchy amount to changing the Canadian Constitution in a fundamental way?

Some believe it does, which makes Prime Minister Stephen Harper's hope for quick passage more of a high-risk procedure in that it might set a precedent in by-passing the provinces on an amendment that some feel requires provincial consent.

Rushing through a change to the office of Queen without due process might also be seen as diminishing the status of the Crown at a time when some of Canada's First Nations are attempting to renew their special relationship with that institution.

The crux of the bill will implement three previously agreed-to rule changes, to end centuries-old practices now viewed as discriminatory:

• male children inheriting the throne ahead of their older, female siblings.
• a ban on a monarch or direct heir to the throne marrying a Roman Catholic.
• the requirement for all descendants of George II to obtain the monarch's permission to marry or else have their marriage declared void.

The third change is thought to affect several hundred people. It will be replaced with a new requirement for the monarch's consent for only the first six people in line to the throne.

Canada's bill will fall in line with legislation now moving through the British Parliament.

U.K. bill went first

British Deputy Prime Minister Nick Clegg, the Liberal Democrat leader who is Prime Minister David Cameron's coalition partner and the spokesman for the U.K. bill, said during House of Commons debate at Westminster last Tuesday that the current rules have "no place in modern Britain" and "reinforce old prejudices and old fears."

Updating the way the Royal Family self-perpetuates became more of a priority after the 2011 marriage between Prince William and Catherine, Duchess of Cambridge, followed by last fall's pregnancy announcement.

The July due date for a possibly female heir to the throne has focused the minds of governments across the 16 Commonwealth countries where Queen Elizabeth reigns.

Prime Minister Harper was among those who unanimously supported the British initiative to pass common legislation to amend the ancient laws — now hundreds of years old — that set out the rules for royal succession.

Cameron's coalition government went first, fast-tracking legislation introduced on Dec.13. The move was not without risks for a Conservative prime minister who does not govern with a majority. Cameron needs to avoid offending his traditional, monarchist base while accomodating the more reformist push of his coalition partners, the Liberal Democrats.

British newspapers have reported that Buckingham Palace is "on board" with the changes, with Clegg saying "extensive discussions were held" about the "very precise" reforms.

The Canadian bill will not mirror exactly the British legislation, but must amend in the same manner the same ancient acts that form the basis of Canada's system of constitutional monarchy.

Canada's legislation was still being drafted earlier this month.

Canada has independent Crown

At the time of Confederation, the British North America Act that joined Canada's first four provinces described them as "federally united into One Dominion under the Crown of the United Kingdom of Great Britain and Ireland, with a Constitution similar in Principle to that of the United Kingdom."

But Commonwealth countries such as Canada officially got their own heads of state when the British Crown became divisible with the passage of the Statute of Westminster in 1931.

Since they all observed the same rules for the line of succession in the years since, all 16 countries continue to have the same person, Queen Elizabeth, as their monarch.

At the Commonwealth Heads of Government meeting in Perth, Australia, in October 2011, all agreed to act in tandem to modernize the rules.

New Zealand is coordinating the effort so that legislation passed in the separate legislatures all comes into effect simultaneously.

It's not a simple task: while all governments provided their written agreement by Dec. 2 to all three changes, the distinct processes for each to make the changes official have their own possibly tricky elements.

"The steps needed in each realm to implement the agreed changes, including any legislation, depend on the constitutional situation in each realm," explains Rebecca Kitteridge, the secretary of the cabinet and clerk of the executive council in New Zealand, who is working with the U.K. and other countries to coordinate things.

• Related: Will the British throne cut its ties to the Church of England?

"Those realms that intend to legislate will need to follow their own legislative timetables," she wrote to CBC News. "It is intended that all of the legislation, including the U.K. legislation, will be brought into force at the same time."

Kitteridge confirmed the changes will apply to any baby born after the Oct. 2011 Perth Agreement.

Provinces not weighing in (yet?)

British Deputy Prime Minister Nick Clegg (l) and Prime Minister, David Cameron (r) laugh during a joint news conference earlier this month. Clegg is the spokesman for the Cameron government's bill to change the royal line of succession. (Peter Nicholls/Pool/Reuters)

For its part, the Harper government does not appear to have consulted with all, or perhaps any, of its provincial counterparts before providing its assurances the rule changes would pass.

"We have not been contacted to date and Ontario has not considered the question of the appropriate process to change succession laws in Canada," Neala Barton, a spokesperson for the Ontario premier's office wrote to CBC News last week.

"That said, we are not aware of any reason why we would oppose changes to succession laws that are necessary to keep Canada in line with changes adopted by the British Parliament."

Any province that wanted to raise a fuss about the need for provincial consultation has a legal precedent to argue: a 2003 ruling from the Ontario Superior Court of Justice found that the 1701 Act of Settlement — one of the ancient laws the bill would amend — is "part of the laws of Canada" and the rules of succession are "by neccessity incorporated into the Constitution of Canada."

And here's the sticking point: section 41 (a) of Canada's Constitution, patriated in 1982, says that an amendment in relation to the office of "the Queen, the Governor General and the Lieutenant Governor of a province" can be made only where authorized by "resolutions of the Senate and House of Commons and of the legislative assembly of each province."

So does that mean reforming the rules about who can be king or queen requires unanimous consent from Canada's provincial capitals?

Saskatchewan's view, shared with CBC News last month, is that this bill doesn't amount to changing the Constitution, in that the Constitution simply defines our monarch as the monarch of England, whoever that is.

Another Atlantic province shares the legal view that provincial consultation is not necessary, because these changes simply maintain the symmetry of succession that currently exists with the United Kingdom and the other realms.

The Parti Québécois government in Quebec — not always a bastion of monarchist support — has yet to join the conversation.

A spokesperson for the federal justice minister said in an email to CBC News following publication of this story that the department's legal advice is a constitutional amendment is not needed for Canada to consent to the proposed changes.

But what about Canada's sovereign Crown? If this spring's process doesn't treat this amendment as a Constitutional reform, does that diminish what the authors of the 1982 Constitution intended?

"I'm not sure the provinces have thought through what kind of precedent it sets," says University of Ottawa professor Philippe Lagassé.

He suggests that if the provinces overlook their constitutional right to weigh in on this matter then that could give the federal government a "free hand to do other things [without the provinces' consent] in the future, citing this as a precedent."

• Related: The 'royal pandora's box': are these changes a slippery slope?

With First Nations raising the historic and legal importance of the Crown in establishing their treaty rights over the course of the recent Idle No More movement, it would be odd for MPs to be seen as diminishing the significance of changes to the Crown's line of succession by not fully consulting on and debating the bill, he suggests.

Lagassé says it would be "inherently dangerous" for Canada to be seen as simply going along with the British legislation.

However, "my sense is that none of the parties see this as a fight worth having," Lagassé says, noting that Opposition Leader Tom Mulcair, despite his Quebec origins, doesn't seem keen to engage.

The constitutional limits of what the federal government has the right to change on its own need to be tested, Lagassé suggests, which could prompt someone to bring a court challenge.