A private letter written by Canada's first prime minister in 1867, shortly after the British North America Act was signed, is going up for auction Friday in Toronto.

The eight-page letter, written to English legal theorist Sir Henry Sumner Maine, is of particular significance because Sir John. A. Macdonald penned it shortly after Queen Victoria signed the BNA Act, which confirmed the Canadian Confederation and served as the Constitution until the Canada Act of 1982.

Sir John A. Macdonald's eight-page letter says, in part: 'I sail in four days for Canada with the act uniting all British America in my pocket.'
(Heffel Fine Art Auction House)

The letter could fetch $60,000 or more, according to Andrew Gibbs, the director of appraisal at the Heffel Fine Art Auction House, which is selling the letter for an unnamed owner in Ottawa.

But pinpointing an exact price is difficult because of its rarity. A letter written from the Plains of Abraham — the decisive battle in the Seven Years War that brought what is now Quebec under British rule — sold last year for $60,000 US, Giggs said. And similar letters written by U.S. presidents have gone for as much as $100,000.

Among the key lines in the witty and upbeat letter is Macdonald's summation of his work in creating what would become the nation of Canada.

"I sail in four days for Canada with the act uniting all British America in my pocket," he wrote.

But what might make the letter of particular interest to a U.S. buyer is Macdonald's quip at the end of the letter about an invasion of San Francisco.

"A brilliant future would certainly await us were it not for those wretched Yankees who hunger & thirst for Naboth's field," said Macdonald, making a Biblical reference to stealing someone else's land.

"War will come someday between England & the United States and India can do us Yeoman's service by sending an army of Sikhs … across the Pacific to San Francisco and holding that beautiful & immortal city with the surrounding California — as security for Montreal and Canada."

Gibbs said the idea of invading San Francisco was "perhaps tongue in cheek" on Macdonald's part.

The prime minister also discusses the difficulties involved in combining French civil law with English law and asks Maine to recommend a place in India where his cousin might set up a fledgling law practice.

The letter has had private owners throughout its history but is in remarkably good condition, Gibbs said.