What does it mean to "surround Canada" and why would anyone want to do it?

Almost the entire population of Canada is huddled against the US land border. Greenland is very far away from where the action would be if the US "takes" Canada. There would likely be few shots fired; Canada lacks the ability to put up a credible defense. The EU has no capacity to resupply Canada in any case. The whole scenario makes bizarre assumptions.

I don't think most Canadians consider the US "taking" Canada to be a serious scenario outside of echo chambers among the "too online" crowd. What would that gain the US that it doesn't already have?