Frankly, the US doesn’t need to grab all of Canada in this scenario. They just need Halifax, because that’s the only port through which the British can ship men and material in amounts to matter. No St. Lawrence Seaway yet, after all. Then they might be able to make a deal with Canada.
Now, whether the US will be able to pull this off early is an open question...
Now, whether the US will be able to pull this off early is an open question...