Whenever we get to the New York street photographers (Robert Frank, Gary Winogrand, et al) in my History of Photography course, a discussion about taking pictures of people without asking their permission always ensues. This article below, from the Blouin Art Info website, is based on American law, but I don't think Canadian law differs much on this matter — if it's for art, your mug is fair game.
A Photographer's Artistic Freedom versus an Individual's Right to Privacy
I chose a photograph by Bruce Gilden because he has such an in-your-face style of photographing, and he certainly doesn't ask for anyone's permission before he snaps the shutter. Check out the clip below to see how he works. Goddess forbid that I should ever end up in one of his photos, even if it is for the cause of art!
WNYC Street Shots: Bruce Gilden