As king27 mentioned, Discovery is not widely accepted in Canada. Make sure to have a Visa or Master Card for fuel, etc.
Northbound I will stop at the first Canadian bank and use their ATM machine to take out $400cdn, which normally will last us till we get to Alaska. Then we do the same on the south bound leg of the trip. On the way back south I will try to use up any of the remains Canadian currency for fuel etc.
Canadian banks and merchants are much better at working with US currency than once back in the US and trying to use Canadian dollars. I think I have about $40 cdn remaining from the last trip and will take that back north the next time