The problem is that there is a not-insignificant number of people that want the US to annex Canada.
In the US, about 15% of Trump voters would support annexation of Canada, even if Canada didn't want it. That's about 1 in 7.
https://vancouversun.com/news/trump-51st-state-most-americans-have-no-interest-in-canada-annex
The disturbing thing is that about 18% of Canadian Conservatives would support annexation. That's almost 1 in 5. Most of us know five Conservatives, so chances are you know someone who is essentially a traitor. I think Conservative supporters need to be aware that this is the company they keep.