Ha-ha, just kidding, but made you look, because you're looking for a reason. Or is the consolidation of power a good enough reason?
It's hard to see any other reason, especially for a conservative leader like DonJohn, to want Canada to join the US. The conservative party here in Canada understands climate change for what it really is (even those in the oil industry), so to DonJohn, Canada should look like a whole bunch of liberals. I mean, politically, Canada is not all that different from California and he doesn't seem to like California that much. Not only that, it's far colder than California. And on top of that, there are millions of people here speaking French. Add it all up, and Canada just doesn't really seem like his thing.
I'm not sure why people, myself included, thought he was kidding? I mean, DonJohn is known for a lot of things, but his sense of humour is not one of them.
"Make America Great Again" should now be understood for what it is. This slogan never really resonated with people who've always though the United States was pretty great. But now it is clear that "Make America Great Again" means wielding power with regard for no one's interests but our own. "Restoring the world's respect for the United States" means making other countries kowtow to the US. It's all about survival of the fittest now. Sorry Ukraine (and maybe Lithuania?), Russia is bigger and more powerful. Same for you, Palestine. It shouldn't take more than a generation for people to fall in line with a new world order.
DonJohn is serious. He actually does want to take over Canada. And Greenland. And Panama. He'll convince his followers that it's for our security, the classic argument for making a pre-emptive strike - pitch it as self-defense.
America has been the greatest country on earth, but not by being an aggressor. Take a good look at the faces of all our Olympic team, with so many gold medal winners, and you'll see what has made America great.