Were you trying to pay with US money or Canadian? Near the border in places like Vancouver, the Gulf Islands, Nanaimo, etc. most places take either one. The exchange rate is almost at par right now. The Canadian dollar is worth a bit more but not enough to bother with so the merchants, marinas, grocery stores, etc. don't care what you pay them in and they give US money it's face value (no exchange rate).
But more inland in places like Quesnel it might be more of a big deal with the local bank branches so stores and restaurants may be a lot more reluctant to take US cash.