It all comes together when you remember he's acting on orders from Putin to weaken his own country. Some of the first actions he took were to A) Stop helping Ukraine to take strain off Putin, and B) Start weakening the US economy by angering trade partners. Canada is the biggest trade partner of the US so naturally we got hit first and hardest.

But the US is the land of greed and maximum profit so they don't actually make much there any more. Canada has a healthy internal economy that just got a big boost from lowered inter-provincial trade barriers whereas the US does not do as much trade internally. They rely heavily on imports of goods and raw materials, especially from Canada.

Canada will hurt from this but we have materials and the world is full of customers, so we can adjust strategy and adapt. The US? They need to buy these materials and they just gave the middle finger to the entire rest of the world. The US will hurt so much more in the long run, and I'm sure that is entirely why Donald is doing this. Even if the US were to invade it still wouldn't fix their shattered economy as all trade with Canada would cease and they would have to find a way to obtain said materials and send them south all while fighting a multi-million strong resistance that would likely be assisted by foreign powers. All while their own economy would collapse and internal unrest might turn into civil revolt or even civil war. None of the states that border Canada are going to want a conflict on their soil and border cities are so close together that US citizens will suffer too.

There is no situation where the US walks away as a winner, but I'm sure that is exactly what Putin ordered. This is a highly planned attack on the US by itself, taking pressure off Russia and leaving the pacific open to China.