In MN you can obtain an "enhanced driver's license" in lieu of passport or card; price is $30-40 dollars.  Since I only plan to travel to Canada I will go that route.  I do not know if you can get this type of DL in other states.  Rules on the DL are also for entering Canada by water or land transport and NOT by flight.
So I cannot answer the bush plane question but wanted to let those who did not know of the EDL about it.  Also still need the RABCP if planning to cross/recross the water border during your travels; otherwise the rule is to check-in at customs IMMEDIATELY when returning (which is of course not possible if you are several days into your trip and nowhere near a customs office.