In the weeks following the al-Qaeda attack on the World Trade Centre, sales of the tranquillizer Xanax shot up 22 per cent in New York and, in many respects, America's collective anxiety level never seemed to go down.

Today, the U.S. fear of another terrorist attack is transforming the U.S.-Canada border.

In February, the U.S. Customs and Border Protection agency began patrolling the North Dakota-Manitoba border with the first of what is expected to be a fleet of unmanned aerial reconnaissance vehicles — drones that cost roughly $10 million apiece.

And now, as of June 1, Canadians wanting to enter the United States at one of the 94 land crossings will no longer be simply waived through after a short chat with a U.S. border guard, or a quick glimpse at their birth certificates or driver's licence.

Beginning June 1, 2009, all Canadian visitors to the U.S. will require either a passport or an enhanced driver's licence, like this one shown here by Quebec Premier Jean Charest. Four provinces - Quebec, Ontario, Manitoba and B.C. - are planning to produce these enhanced licences or an equivalent, which emit an electronic signal that broadcasts personal data of the holder. (Canadian Press)

Canadians citizens will now have to show one of three documents: a Canadian passport; a credit card-sized piece of plastic, called a NEXUS card, for frequent travellers; or a so-called "enhanced" Canadian driver's licence with a computer chip in it, in the process of being made available in four provinces.

This move is the latest in a series since 2001 (including closer border inspections and the use of tracking technology to monitor the movement of goods and people over longer distances) designed to "thicken" the Canada-U.S. border, as the U.S. Department of Homeland Security puts it.

The goal is to develop what is often called a virtual border involving much more electronic tracking and, ultimately, to keep the bad people out.

For homeland security, the bad people include drug runners and queue-jumping immigrants. But the baddest of the bad are Islamist extremists and most U.S. politicians, it seems, agree with the FBI and CIA that the most likely place for these extremists to launch an attack on United States is via Canada.

Why us?

To Canadians, this fear seems exaggerated, an unnecessary continuation of the post-9/11 anxiety attack.

After all, we don't have much of a terrorism problem here. Since 9/11, two Canadians have been convicted on terrorism charges — Ottawa computer engineer Mohammad Momin Khawaja and an as yet unnamed teenager connected to the Toronto-18 affair.

On the other hand, in 1999 Ahmed Ressam, a member of a suspected al-Qaeda sleeper cell in Montreal, was caught trying to cross into the U.S. at Port Angeles, Wash., with a load of explosives in his car. Ressam was intending to blow up the Los Angeles International Airport.

But since then, there has been no similar infiltration attempts and Canada has spent, at Washington's behest, an estimated additional $2 billion a year on border security, particularly at U.S.-Canada land crossings.

We've even erected anti-terrorist security fences on the docks at tiny ports on the Great Lakes such as Owen Sound.

Scanning equipment, such as these on the U.S. side of the Ambassador Bridge, which links Windosr and Detroit, will read the electronic signals from enhanced driver's licences and other data-emitting cards. (Carlos Osorio/Associated Press)

So why do prominent U.S. politicians, such as President Barack Obama's new homeland security chief Janet Napolitano, keep looking northward and repeating the annoying myth that some of the 9/11 hijackers infiltrated the U.S. through Canada?

Are we really North America's weak link?

Too multicultural

Clearly Napolitano had her facts wrong about the 9/11 hijackers or maybe she just misspoke, when she was interviewed by the CBC recently.

But a former top official in the Bush administration says the threat that terrorists will use Canada as an unlatched back door to America is a real one, in his view, and can't be ignored.

The former number two at homeland security, Stewart Baker says concern that terrorists will use Canada as a staging point is not based on the 9/11 myth or the Ressam example alone but on what U.S. intelligence experts regard as Canada's liberal attitude towards accepting immigrants and refugees from parts of the world identified with Islamist terrorism.

He points a finger in particular at Quebec, which has control over its own share of Canada's yearly immigration quota. In its haste to find French-speaking immigrants, Quebec has accepted many from Algeria and Morocco, Baker points out. Both are countries that have had their problems with extremists.

New arrivals from East Asia and, in particular, Pakistan are another concern.

Sharing information

In addition, Baker claims the U.S. has had to reinforce its side of the border because Canada refuses to share vital information gathered by Canadian intelligence agencies on suspected terrorists living in Canada.

It is hard to believe we are not sharing this information, Canadian intelligence agencies have always boasted about their close relationship with the U.S. Though perhaps the sour taste following the Maher Arar incident has led Canadian agencies to be less forthcoming than in the past with their unfounded suspicions.

Baker also cites what the U.S. considers Canada's lax regulations over visitor visas.

Before the U.S. will grant a foreign country the privilege of having its citizens enter the U.S. without having to obtain a visa, that country has to agree to do a criminal and security check on any individual wanting to go abroad and share the results with American border authorities.

Countries as diverse as Latvia and South Korea have agreed and Canada has a visa-waiver program, too.

But, according to Baker, Canada's program does not require mandatory criminal background checks and so U.S. authorities fear the possibility that terrorists will try to take advantage of the less rigorous Canadian regulations and then try to sneak over the border into the U.S.

That is the basis for the much tougher border-crossing rules that begin on June 1.

Baker remembers learning the proud boast taught to school children in both countries — that Canada and the U.S. had the longest undefended border in the world.

Baker insists that's still true. After all neither country has moved its tanks up to the border.

But it's a new and more dangerous world and this "thickening" of the border will make it more difficult for potential terrorists, the U.S., at least, believes.

And even if Canadians think the U.S. is overreacting to 9/11, Baker, for one, says the anxiety Americans feel that terrorists are determined to do them harm is still very real.