Yes, but most of that is mostly empty space. Occupy a strip of Canada a hundred miles thick along the US border, and you’d pretty much de facto own the rest of the land. The northern communities are incredibly isolated, and dependent upon food shipments for survival. Embargo those shipments for a few months and they’d likely come around.
Militarily, the only way to prevent the conquest of Canada would be if we proactively invited the UK and other NATO countries to establish large military bases prior to the US invasion. Such an invasion will likely require a lot of propaganda build-up, which gives us some time to do this. The hope would be that this build-up convinces the US to back down.
But even in that scenario, if the US doesn’t back down, it just delays the inevitable. Even with large forces in place, supply issues would eventually doom the defense of Canada. It would be far too easy for the US to cut-off resupply efforts, and Canada doesn’t have enough native munitions industry to supply the forces ourselves.
And the attempt to defend ourselves will result in the large-scale devastation of all our cities. Even a “small” war will destroy our infrastructure, and leave us living in the ruins. Maybe the US helps us rebuild, or maybe we end up in refugee camps.