I don't know the legal situation in Canada; I know some things about the situation here in the states. Essentially, if you take photographs here in the U.S. in PUBLIC places, you are okay legally, *unless* you use them in a commercial way. This would not include using them either as news or as art. (News and art are almost always okay, as protected free speech.)
If you use them commercially (think, "as a commercial") then you can get in trouble. For example, if you show a young Mom with her beautiful young child running along a beach, and you sell it for a Pampers ad, you could get sued, because the person in the photo may despise Pampers and can claim that her image has been used to promote something she abhors, and that what you did had nothing to do with news or art, but was simply a way of making money. They can ask for and get a cut of the returns and punitive damages. If you want to shoot this kind of thing, you need a model release.
You cannot take a picture of somebody who has an expectation of privacy call it "art," and get away with it. Say you were invited to a photo shoot (right!) where some of the supermodels were turning their faces to a wall and changing blouses. You get a great shot of "x" with her top off, and sell it as art. Nope. You'll get sued big time. Not only did she have a reasonable expectation of privacy, you're interferring with her business. You'll wind up giving her your film and all prints, all the money you made, punitive damages, and probably her court costs. If the same thng happened on the street, and you sold it to News of the World, then she might be out of luck. It was "news" that a supermodel was disrobing in a public place.
In New York City and other places, if you want to use the sidewalks or the street as a "set," you have to get a permit. This usually just applies to people who are doing commercial photography that requires items (lights, assistants with shades, models, etc.) that will create a disturbance, disturbance being defined as anything that impedes the normal flow of traffic, either foot or motorized. Lots of people ignore the permit requirement and get away with it. The cops'll usually just tell you to move along.
Then there's the practical "thug" problem. Take a picture of a famous piece of architecture, from a public place, which you have a right to do, and the doorman comes across the street, takes your camera away from you and removes the memory card. You call the cops. They refuse to do anything. You sue, and it becomes your word against the doorman, and the doorman says he was just trying to protect the privacy of the people who live in the building, and look what happened to John Lennon. Chances are, you lose, including all the money you paid your lawyer.
Cops will occassionally run you off if they don't like your looks, or if they're feeling like jerks. Resist, and they arrest you on some horse**** charge like disobeying a lawful order and resisting arrest, and they tell the jury look what happened on 9/11.
Most of this, by the way, is covered fairly frequently by PDN magazine (used to be called Photo District News.)
Bottom line: you can shoot anywhere public, as long as you do not create a disturbance, and don't sell recognizable faces for commercial uses. On the practical side, be a little discreet and you'll most likely be fine.
Come to think of it, I do know a little about Canadian law -- their cops seem to be less tolerant than U.S. cops; they really do seem to think of themselves as the "authority." I base this only on my contact with wildlife cops while fishing -- I fish only for muskies, never keep one, have no interest in eating any fish, never drink anything in a boat, and essentially have been discourteously and unpleasantly treated by two or three of their wildlife people, for doing *nothing.* Their attitude is that you're guilty, they know it, and you're just getting away with it this time. Might very well be different with street cops.