Please, when you come to Canada, change your money. It isn't that hard, and it will save me some headaches.
Thunder Bay is close to the border, so we get frequent American visitors to the art gallery. For some reason, they believe it's fine to just hand us American money. Canada's just the 51st state anyway, right? I know that when I go to the States, I don't flash my Canadian cash all around the place. I trade my money in for your pallid green bills.
Our cash register is not a hi-tech computer with a flat panel display and a high speed Internet connection. It's a box with lights and a few buttons. The exchange rate is currently set to about 62 American cents for every Canadian dollar, and our boss has to change it manually. I honestly don't even know how to do the conversion on the machine (there's a button, but I'm never sure when to push it during the transaction...).
So please, take it from someone who has to deal with your cash. I'll be happier if you change it to Canadian money. Our bills are shiny and colourful--you'll like them as souvenirs. And if I'm happier, it means I'll be nicer to you. And if I'm nicer to you, you'll be happier. Welcome to the circle of life.