Opponents of Canada's wide-open immigration policy have good reason to complain. This country embarked on a massive social experiment in the early 1990s, when the Mulroney government opened the immigration floodgates. That experiment is radically altering the ethnic makeup of the population. Yet that decision was never properly debated. Has the time come for such a debate, or is it too late?

A report this week from Statistics Canada forecasting the country's demographic makeup in 2036 suggests it's too late. The transformation of Canada is already far advanced, and continuing. By 2036, the agency predicts, as many as 30 per cent of all residents will not have been born in Canada. Another 20 per cent of the population will be native-born, but with at least one immigrant parent. Since the vast majority of immigrants come from Asian or Pacific nations, within 20 years Canada will likely be as brown as it is white.

Some old-stock Canadians, as Stephen Harper called them, will resent this. No one asked them, they will say, whether they wanted the European, Christian country they grew up in to be transformed into something so cosmopolitan. They lament the loss of traditional values and social solidarity. Some of them look with envy to the United States, where Donald Trump surfed nativist resentments all the way to the White House.

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But a Canadian Donald Trump – at least one who wins a general election – is unlikely. There is no future courting the angry white vote. There just aren't enough angry white voters.

Some Conservative leadership candidates are flirting with nativism nonetheless, because the Conservative Party membership is older and whiter than the general population. But, in fact, Conservatives should welcome immigrants. The Philippines, India and China accounted for 40 per cent of new arrivals in 2015. They are economically and socially more conservative than many of the native-born; many of them voted for Mr. Harper in 2011, and they are a natural constituency for the Conservative Party.

Justin Trudeau, however, won suburban ridings with large immigrant populations across the country in 2015. Politically, keeping those voters loyal is his first and most important task. Winning them back should be the first and most important task of the next Conservative leader.

The massive demographic shifts under way in Canada speak to both growth and decline across the country. In 2036, StatsCan predicts immigrants will make up at most 10 per cent of the population in New Brunswick and Nova Scotia. About a third of Montreal's population could be immigrant, but in the rest of the province they will be hard to find. In Ontario and British Columbia, about a third of the population will be foreign-born, and Alberta should be near 30 per cent.

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In terms of both population and politics, Canada will be a country of large, growing, young, diverse cites, with everything in between older and whiter and continuing to decline.

Quebec will struggle to make its voice heard: those whose mother tongue is French will decline from 21 per cent of the population today to 18 per cent in 2036. The number speaking English as a native language will also go down, but up to 30 per cent of Canadians will have a mother tongue that is neither English nor French.

Canada is losing its old-time religion. Ninety per cent of Canadians identified as Christians in 1970. Today, it's two-thirds, and will be just over one half by 2036. Christianity is not being displaced by other religions – only 7 per cent, at most, will identify as Muslim by 2036 – but by no religion at all. A quarter of all Canadians today identify with no faith, and that number could reach a third by 2036.

The fact that this country has deliberately transformed the makeup of its population in a way no other country has managed, or even attempted, speaks to the tolerant, diverse society in which we live. Multiculturalism works and Canada is proof.

If you're grinding your teeth at this, if you long for the Canada that was, it's easy to understand your frustration. That Canada has gone away. By 2036 it will be barely a memory.