I would not exchange money at the border going into Canada. Wait till you get to a larger town and then go to the bank and ask to exchange your US greenbacks for Canadian. We got the best deals right from the banks last year when were in Canada, or used ATM to get local cash.
We try to use credit cards/debit cards for fuel and large purchases, but always had enough to fill the RV in cash if needed.
Just be aware that in Canada that $1 is a gold coin (Looney) and they also have a $2 coin that is silver and gold. They don't use $1 paper money.