Canada here, but more specifically Saskatchewan. (Different rules seem to apply in different provinces in my experience.)
Basically at restaraunts the general accepted rule is 10-15% for mediocre service.
e.g: If the waiter/waitress pays sufficienct attention to your group that you dont run low on drinks and stops by to ask if you need anything occasionally. (Say three times during a meal)
If the service is exceptional i will tip upwards of 25%.
e.g: if they make a conscious effort to go out of their way to make sure you have everything you need, and notice things you might need (like more drinks, condiments, fresh napkins, clean ashtrays, etc...) even before you think about asking for them. Also if they pay direct attention to how you are enjoying your meal and try to make it better without making it seem like chore or that it is inconveniencing them. (Like special food/diet requests or altering their menue to suit your specific taste.)
I have not tipped at all at restaraunts before but i can prolly count the number of times on one hand. I have to find a darn good reason not to. Like the server pissed me off, was aloof, or just didnt give a chit. Even in these cases i will most often leave a small tip anyway because maybe the server was just having a bad day...either at work or other stuff going on in their lives.
At bars it is a different story though. If i am sitting at a table i will leave a change tip like nilsen mentioned for the waitress if she does her job. The amount i tip has nothing to do with what the waitress look like or how "chatty" she is with me. I know im not going to get anything if I tip 5 bucks instead of 1 or 2 so i base it on job performance only.
If i am sitting at the bar i rarely tip. (Sorry tapa.) But that is because I usually take care of myself. I will get my own ashtray, clean up any overpours myself and if I am just drinking coffee I even get up and get my own refills. Hell i have even poured pints for myself the odd time when the bartender was busy. This, because I always go to the same pub and know all the staff there and I am friends with a few of them outside of work. Because I dont really demand anything from them I dont really feel the need to tip, nor do they expect it.