Here's the thing: That "Golden Dome" Trump is talking about needs to have facilities in Canada to work. If they only have them in Alaska and their northern states, they won't have enough time to track or engage possible missile threats. So, he can blather all he wants about Canada wanting to join in, the reality is they need us more than we need them. It's just like the series of radar stations they built in the 50s to counter the Soviet threat. They were mostly on Canadian soil.
I think we (well, anyone who isn't in the right-wing cult) knows Trump is delusional. He says these things hoping if he says it enough it could happen. But, the vast majority of Canadians despise Mango Mussolini.
Now, I seriously think Trump is hoping to get Canada and Greenland to join the US for a few reasons. First, there are the vast natural resources in the Arctic, and strategically, it could be an important waterway if the ice caps continue to melt...
BUT....I really think the real reason is he wants to have a legacy. I think he probably knows that he will be remembered as one of the worst presidents in US history (cue the righties to defend him...), and once he is dead, the MAGA cult will pretend that they never supported him...He might go down like Rush Limbaugh, someone who dominated the culture, but once they were gone, nobody really thinks of them...