That was my very first thought. Although depending on whether the Loonie dollar exchange rate is running up or down some places, North or South, may want you to cover it.
Yep, that happens on both sides of the border; depending on the amount and the rate you may get a better deal from a bank or currency exchange. The latter will usually give you a better rate than retailers, but the savings are offset by a per-transaction fee.
Back in the days when our dollar was below 80 cents, a lot of shops and tourism operators (especially in Florida) would accept our dollar at par to hang onto our business.