I do not really understand this line of thought of USA invading Canada. What’s in it for them? Canada isn’t some helpless third world with oil that they can exploit, Canada can and will retaliate.
Canada can retaliate in a trade war, but if it is real annexation/invasion, Canada cannot effectively fight back. It would be a walk in the park for the US. We do not have the military resources, our popular is 1/10 the US, and our weapons are mostly supplied by the US, so they may not even work in a real war. And unlike with the Russian invasion of Ukraine, no one is coming to our aid.
Also the US would likely do it incrementally and start with a friendly province like Alberta, where a significant minority may even welcome it.
Certainly Iraq pre-invasion made them look like a pushover!
That's not to say that invading would be painless, but let's not pretend that Canada would have a chance.