Canadians appalled by the violence in the Oscar-nominated film 12 Years a Slave probably also feel proud that the carpenter who helps Solomon Northup regain his freedom is Canadian (and played by Brad Pitt). We've all heard that Canada's only role in the slave trade was to hasten its end; but long before the underground railroad got started, colonial Canada was a safe place to buy, sell and own slaves.

For about two centuries, slavery was legal in New France, and in Lower Canada under British rule. Captive human beings were owned by people from almost every level of society, including governors, bishops, military officers, merchants, priests, blacksmiths and tailors. James McGill, founder of McGill University, had slaves. So did Marguerite d'Youville, the Grey Nuns founder who was canonized in 1990.

The shocking details are all laid out in a book by Quebec historian Marcel Trudel that has just appeared in an English-language paperback as Canada's Forgotten Slaves: Two Hundred Years of Bondage. Mr. Trudel, who died in 2011, shreds our national myth about slavery by naming hundreds of eminent and ordinary Quebeckers who were eager to get slaves and proud to flaunt them before their neighbours. People went into debt to buy them.

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"Slavery in Quebec was not some economic imperative, but rather a form of public extravagance which conferred prestige," Mr. Trudel writes. In 18th-century Quebec, whose boundaries reached into parts of what is now the United States, a slave was a status symbol, more often found in town than in the country, more likely to be a domestic servant than a field labourer.

Mr. Trudel provoked a scandal in Quebec in 1960 when he first published his revelations as L'esclavage au Canada français. Generations of historians and church leaders had nurtured the myth that slavery, if it had existed at all, had been imported into the province by the English after the conquest of 1760. In fact, 85 per cent of Mr. Trudel's confirmed owners were francophones, and the Quebec slave trade was well established before Wolfe met Montcalm. Nobody could refute Mr. Trudel's careful research, so he was ostracized professionally, and in 1965 left his post at the University of Laval for a less frosty berth at the University of Ottawa.

The number of slaves Mr. Trudel could confirm from archival records was relatively small – about 4,200 in all, compared with the 250,000 who toiled in the French West Indies in the mid-1700s. Canadians never knew slavery on an industrial scale, only because they never convinced big-time slave traders that it was worth sending African slaves on the longer shipping route to Montreal or Quebec City.

Many in Quebec had to be content with captives stolen or bought from indigenous peoples, some of whom practiced slavery before the Europeans arrived. About two-thirds of the slaves in Quebec were native people, mostly from the Pawnee nations of modern-day Nebraska, whose French Canadian name – Panis – became a synonym for an indigenous slave of any origin. Black slaves were known as bois d'ébène (ebony wood), or pièce d'Inde if they were in prime condition. Blacks, being harder to get, were about double the cost of indigenous merchandise. Slaves of all kinds were sold at auctions and advertised in newspapers, including the Montreal Gazette, which had slaves in its print shop.

The legal and religious basis of the enterprise was conflicted. Louis XIV granted a petition to permit slave ownership in New France in 1689, even though it was not allowed in France. The church insisted on baptism and Christian burial for slaves, but ignored Pope Paul III's 1537 decree that indigenous peoples in the Americas should not be enslaved "in any way." Many major religious orders in colonial Quebec, including the Jesuits, owned slaves. Marguerite d'Youville was even taken to court by a Montreal doctor who claimed she had, in the night, spirited away a Panis that belonged to him (the trial's outcome was not recorded).

The House of Assembly in Lower Canada dithered for years in the late 1700s over motions to abolish slavery, probably because several members would have been directly inconvenienced. But the last recorded slave sale in Quebec occurred in 1797, and Britain abolished slavery in most of its empire in 1833, just as traffic on the underground railroad to Canada was nearing its peak.

In the decades since Mr. Trudel's book first appeared, a secular form of Quebec nationalism has found its own reasons to forget the province's slave-trading history. Montreal historian and journalist George Tombs, translator of the revised edition of Mr. Trudel's book into English, got a good demonstration of the new amnesia when he mentioned his project to an acquaintance who happened to be a former Parti Québécois cabinet minister.

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"He got quite annoyed, and said 'You shouldn't be translating that book!'" Mr. Tombs recalls. "His problem basically was that it would give a bad image of Quebec. Pauline Marois has been saying that we have to make sure that everyone knows national history, but there's a big part of national history they're not going to learn."

That doesn't explain why Mr. Trudel's pioneering book had to wait more than 50 years to become available in English. Mr. Tombs says it's partly because Canadians are accustomed to getting our history "in little bits and pieces, depending on which region the historian is from and which political agenda the historian is pursuing."

Several historians have written more recent papers and books that focus narrowly on slavery in Nova Scotia, Prince Edward Island or Upper Canada, where loyalists from the American colonies often arrived with their human chattels. What's still needed, Mr. Tombs says, is a broader telling of the Canadian slavery story that we can all come to grips with. If, as Prime Minister Stephen Harper has said, Canadians need to know their history better, they should know the bad bits, too.