How would his effect the course of the war? Would the US attack Montreal first?
Possibly. It really depends on how the war effort elsewhere is going, though. For example, if the Brits/Canadians end up going thru Michigan, we might have to defend the Detroit area, then engage southwest Ontario first, in that scenario. Or, in another, we might end up invading the Maritimes first, most likely thru New Brunswick via Maine.