That actually is not a bad idea...
I figure it could be broken down in 3 different ways:
Option 1: An alternate history scenario, which takes place during the Great Depression, where a more militarized Dominion of Canada, and the United States go to war, following a sneak attack by the U.S. in an attempt to stimulate the economy and national pride. Main combat revolves around RCN/USN conflict on the "Lakes".
Option 2: A future scenario, in which a Canada, which has moved back to its more traditional conservative roots, goes to war with an increasingly liberal United States. The lead invasion comming up from Michigan.
Option 3: A near future scenario, in which the US invades Ontario/Loyalist Canada, following its fracture, with both Western Canada and Quebec gaining their independence.