After numerous trips to the US and Canada, we personally feel comfortable leaving a 15-20% tip (of the pre-tax total) and have always treated tipping as part of the cost of eating out. We use this percentage as a general rule any time we are provided with a service, so this would include bars, pizza delivery etc.
Tipping is also expected in hotels, when staff bring luggage to a room or you make use of the valet service. We tend not to make use of these services, but if we did we would pay the luggage handler $1 for each case and perhaps a couple of dollars to cover any smaller bags. We also leave a tip for the chamber maid when we stay in a hotel, usually a couple of dollars per night, depending on length of stay and service.
Tipping is also customary for other service providers such as hairdressers, manicurists, and taxi drivers. In these cases the percentage of tip is really up to the individual, but a 10% minimum is common.
Tipping is not a requirement in some counter service shops eg. coffee shops, ice cream shops, cafes, although “tips jars” are often placed on the counter tops to make you feel you should. It is really not necessary and purely your choice.
You would not tip in supermarkets when they pack your shopping and/or bring it to your car.
Generally waiters and waitresses are not paid very well in Canada so they rely on tips. Perhaps this also forces a better service in restaurants as they really need to earn that tip? Sometimes, the service is not worth a tip, but most of the time it is.
If in doubt, ask the service provider what the norm is. We have found most people to be pretty honest and we have had people refuse tips where it isn’t expected.
Links that outline the tipping system:
All this said, at the end of the day tipping is an entirely personal choice.