I was at R de C last year and noticed guests were tipping in CDN toonies and loonies. The gesture is gracious, and appreciated I'm sure, but the employee can't cash them in at a bank without a huge service charge, if at all. Leave your change in your pockets. A nice thing to do is to ask your favourite bartender a few days before you leave if he has any Canadian change and offer to exchange for pesos or CDN bills and YOU bring it back. Just something to consider.