Trump’s knowledge of his own country’s history is not very sound. If it were, he’d know that America tried to annex Canada once before, in 1812, and failed. This was because the Canadians resisted then, as they appear to be doing today.
Americans (that is, US Americans) sometimes refer to The War of 1812 as their ‘Second War of Independence’; but that is nonsense. You might just as well call the present war in Ukraine a fight for Russia’s independence. (Indeed, there’s an argument for that.) Back in 1812 the Brits, with colonial and also native American help, were only fighting to save their bit of the North American continent. And it’s probably good that they did; otherwise we wouldn’t have present-day Canada to act as a counter-weight to the excesses of the Great Republic, and of its current President.
British imperialism is conventionally reckoned to have been a thoroughly bad thing. But in certain circumstances – usually when it mainly impacted on white colonial subjects – liberation from British rule, or from British protection, could have its downsides. Canada’s separation from the USA made little or no difference to its people’s ‘freedoms’ overall – British imperial suzerainty was a very light, indeed almost non-existent, burden; and it also meant that it preserved some British governmental and social institutions there, which are likely to have informed the Canadian people’s present sense of difference from their southern neighbours. Looking at Canada from over here in Europe, most of us – and not only her Commonwealth partners – are more likely to identify with her than with the USA. Canada’s Parliamentary system – I guess that government by ‘executive order’ would be next to impossible there – and its very different healthcare system, may be crucial factors here. Trump’s myopic, real estate-capitalist view of the world probably blinds him to these kinds of factors. And also perhaps to Canadians’ very unTrump-like ‘niceness’ (in my experience, anyway). But they will be crucial, I imagine, to Canadians’ reluctance to becoming his ‘beloved fifty-first State’.
Perhaps the USA could become Canada’s ‘beloved’ eleventh (or is it fifteenth?) Province’. That might stem the flow of Americans (Harvard academics, for example) currently fleeing there. When Harvard College was founded, after all, it was still British.