@AlexanderVI understood!
I think our only win condition is surviving long enough that the invader loses their will to continue the war and comes to the negotiating table.
I think holding US territory would be bad for US civilian morale. It would concentrate American firepower on troops in Minnesota, Idaho and Northern Maine rather than on the GTA.
It would also give us something to take to the table. Exchanging territorial gains and returning to pre-war borders would be a good outcome for us.