You must be American, this scenario is outself the realm of possibility.
If I put on my realpolitik hat though, it makes sense why Trump & friends want Canada, same reason they want Greenland: access to the Arctic. Look at a world map and how Canada and Greenland are placed relative to the US. Trump is a real estate guy and lots of land is always the best thing to have.
For Greenland, the United States has no need to flex its military muscle if they want to take it over. The Greenlanders want to be free from Denmark and this is a great opportunity for them to achieve that.
Possible timeline of events:
* Greenland leaves the Danish Realm
* Greenland becomes sovereign nation
* Greenland enters Compact of Free Association with the United States (similar to Kiribati and Micronesia) - boom, best of all worlds for the USA. Juicy real estate, military boost, a local indigenous population that will be able to do nil about it.
* With Greenland secure, the United States finds a pretext for NATO withdrawal.
* The United States either pressures Canada into joining the US or invades outright. European partners do not come to Canada's defence and NATO is officially over. Maybe a European version of it rises in the aftermath.
From there, hard to say what will happen. I would be worried if I was an Icelander.
The thing that would for sure not happen is Canada becoming an actual state in the US. Way too liberal for that and logistically it wouldn't make sense.
> Greenland becomes sovereign nation
Greenlanders don't want to become part of the USA afaik, but they know that in the current situation becoming independent means being invaded, sooner or later, by the USA, Russia or China, so I think that the scenario of Greenland trying to become a sovereign nation is less likely now.
As for Canada, although there are a number of Trump supporters that foam at the idea of invading their neighbor, I think that the invasion would be deeply unpopular (a number of people voted for Trump because he was supposed to stop the wars, not start new ones), especially if the Canadian population offer some kind of resistance although who knows, it is just a matter of enough propaganda...