Well, I have no clue on the situation in Canada with pricing, availability, etc. so I'll just recommend away anyway
- Flower is of course an absolute must, you must get it, even if it's not the title with the most longevity. It's downloadable though.
- LittleBigPlanet is recommended both for it's very fun coop, and for all its online levels. Despite all the crap that people build, some levels are exceptionally well made and will add quite a bit of longevity to the game. It should be pretty cheap as well, if Canada is anything like the rest of the world.
- Critter Crunch is another downloadable game I will recommend heartily. It's a puzzle game with both great singleplayer and great multiplayer, both online and offline.
- You should also be able to find Ratchet & Clank Future: Tools of Destruction at a low price. If you like it, Quest for Booty should be next and finally, A Crack in Time, which is by far the best PS3 game in the series.
- Uncharted. Great games, pretty self-explanatory I'd say
- Batman: Arkham Asylum. I honestly can't believe you don't already own this, it is a fantastic game.
- inFamous is also a very good game, I certainly liked it a lot for its comic book style.
There, ask away for more