I like to idly game this out because it truly reflects how narcissistic and uninformed he is. So, he's talking about admitting Canada as a single state. Lets assume somehow that happens, even though the Canadians themselves would undoubtedly push for as many states as possible if joining the US were the only option.

You've now got a new largest state by both population and area, and one that has ridiculous reserves of resources and a coast-to-coast infrastructure. It instantly becomes the most important state. It's also full of millions of people who didn't want to be Americans and who've had a hundred years of more progressive governance than the US. Congratulations, Republicans, you've just skewed the Senate and completely fucked yourself in the House for a generation or more. You've also got 8 or 9 million Francophones who weren't even entirely sure they wanted to be CANADIANS, much less Americans, to say nothing of being Americans in a MAGA world. This is how real troubles begin.

So, in return for dubious "improvements" to the trade deficit, and certain (what?) administrative conveniences (I guess) for a military that already had basically all the access anyone would ever need, as well as a giant buffer territory you're not politically committed to defending with the same gusto you would your own soil, you completely upset the balance of power in Congress to your own party's detriment and add a huge population that hates their situation. Brilliant.

Although, I guess if you're just done with free and fair elections then a lot of these concerns evaporate...