I would add two/three days and go around lake superior.....that trip is well worth taking.
I would also increase the gas budget.....canadian petrol is alot higher than in the US. Last time we were in nothern ontario gas was 1+ a liter......thats 4+ a gallon. The more remote up there the higher the gas prices, I have seen 2.50 a liter in some areas.
http://www.bankofcanada.ca/fmd/exchange.html will get you the most accurate currency rates of exchange. I usually get the best rate from using my ATM/debit card. Credit cards will hit you with a foreign currency fee that my credit union does not.
Have fun....looks like an awesome trip!