I think its foolish to assume that annexing canada is the same scale of warfare as the wars in Iraq or Afghanistan.

In the case of occupation, american culture is very similar to canadian culture and they will quickly work to control media to paint any insurgencies as violent and terroristic to normal people.

I think canada's best course of action is to be ready to respond to an american military threat. It is far easy to be ready to defend than to spur an insurgency.

America could also bomb us back to the stone age as they've done in other countries by targeting drinking water, waste water, manufacturing, and communications targets. Destroying a couple railway bridges and highway bridges could rip the nation in half trade wise. Even if we mount a succesful insurgency we'd likely have to rebuild from the ashes. I'd rather us come up with a defense plan to prevent that future.