On the eve of Donald Trump's inauguration as his country's 45th president, Justin's Trudeau's office was flagging a speech about Canada-U.S. relations that the Prime Minister made when he was the third-party leader back in June, 2015.

Delivered to the Liberal-affiliated Canada 2020 think-tank shortly before the campaign that would bring Mr. Trudeau to power, the address criticized Conservative prime minister Stephen Harper for letting ideology get in the way of our country's relationship with its most important trading partner. If his party were to be elected, Mr. Trudeau pledged, there would be no "hectoring" of whoever was in charge of the U.S. government; he would build on a proud history of setting aside differences in favour of pursuing shared interests.

So far, Mr. Trudeau seems to be making good on that commitment, even with an incoming president he could not possibly have considered as a potential partner back then. He generally has refrained from public criticism of the White House's new occupant, despite presumable personal distaste for him; meanwhile, Mr. Trudeau's officials and advisers have diligently worked to forge ties with those of Mr. Trump and sell them on the importance of a relationship scarcely on their radar.

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But as speculation about Mr. Trump's presidency gives way to hard reality, we will find out the extent to which Mr. Trudeau is willing and able to stay focused on Canada's economic self-interest – and how much he can tune out voices telling him he should aim for something nobler.

Some of those voices will come from within his own government: Some members of Mr. Trudeau's caucus, deeply uncomfortable playing nice with right-wing populists, would certainly prefer he strike a contrast with Mr. Trump.

Others will come from Canadian media and the opposition. Even before Mr. Trump was elected in November, commentators wanted Mr. Trudeau to upbraid him publicly. Those can be expected to ramp up again soon, and if he declines to criticize the new president strongly for going against Canadian interests on trade policy or to stand up to him on human rights, Mr. Trudeau will be accused of weakness – not least by the New Democrats, who are seeking Liberal vulnerabilities among voters who are opposed to Mr. Trump.

And prominent voices in other countries see him as one of liberal internationalism's few great hopes as a wave of populism sweeps across an increasingly destabilized Western world.

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"I think this is the time for Canada to be loud, very loud, and that's not always the case," was how Ian Bremmer – who heads the global consulting firm Eurasia Group, and is a prominent foreign-policy commentator south of the border – put it in a recent interview in his New York office. Mr. Bremmer, who is friends with Foreign Affairs Minister Chrystia Freeland, said this may be an opportune time for a "Canada doctrine" – echoing a view that Mr. Trump's presidency could help compel Mr. Trudeau to take an outsized role in defending and shaping international institutions.

As seductive as such calls could be for a Prime Minister who unabashedly enjoys the international stage, Mr. Trudeau has thus far rejected them in favour of pragmatism – buying the argument from David MacNaughton, the ambassador to Washington, that Canada's interests (particularly on trade policy) can best be served by acting as a friend to Mr. Trump at a time he will need one. As evidenced by his cancellation of his visit to this week's World Economic Forum in Davos, Switzerland, where last year he was the toast of the town, Mr. Trudeau is clearly aware he risks giving rise to a populist backlash in Canada if he pays too much attention to international elites at the expense of practical concerns back home.

But it was relatively easy for Mr. Trudeau, going along to get along, when Mr. Trump's words did not have real consequences – when Barack Obama was still in the White House and the United States retained its traditional role with NATO and other international bodies, respected Muslims' and other minorities' civil liberties (relatively), pursued a climate-change strategy, did not seek out trade wars, was suspicious of Vladimir Putin, and was otherwise recognizable.

If a lot of that changes, Mr. Trudeau will have to turn a blind eye – and live with accusations of complicity – if he wants to make good on that 2015 speech.

Or most of that speech anyway. Toward its end, he spoke enthusiastically of also working more closely with Mexico as part of a continental strategy. His government followed through on his promise to lift visa requirements that Mr. Harper imposed on Mexicans. But it plainly has little intention of otherwise aligning more closely with NAFTA's southernmost partner when that country is firmly in Mr. Trump's sights.

The Prime Minister's aim, one of his advisers said on Thursday, is for Canada to lead by example on matters such as diplomacy and human rights without ramming its views down its neighbour's throat. But even that has its limits.