A lot of your assets are probably held by vanguard or blackrock, like you own VEQT or XEQT those are their assets, so no those kinds of things aren't going to get seized or anything like that.
Also Canada would be far too large, with far to much support in the US to be kept as a territory. It would be increasing the US population by 10% and be the second largest "state". Guam, PR, etc, are all tiny. Any of this stuff requires an act of congress which isn't going to happen. This is mostly reddit hysteria that is not based in reality.
It's a shame, normally I wouldn't be super opposed to more of an economic union with the US depending on what it looks like, like something like the EU where we keep our own country and laws but use the USD, share defense, more citizen movement between the 2 countries, more aligned taxation, better movement of capital and investment, etc. The CAD sucks and canada can't build a strong economy because of our proximity of the US and the sucking hole of all our talent, our access to capital investment is weak, again because of our proximity to the US, and our military is deeply integrated into the US. But Trump is such an unstable asshole, and their democracy is such a shitshow, that this is not even something I'd be willing to be entertain, I'd much rather us create some sort of integration with the EU now, who also need our resources. Especially as the EU rearms into a superpower.