Unfortunately, FutureShop does not provide a repair service for controllers, and if you had the PSP, it's such a relatively low-value item, that it'd be replaced instead of repaired.
Once you're also outside the first 90 days, which is Microsoft's warranty period on most accessories, the best you can do is drop the cash to pick up a new one. 
I know, not what you wanted to hear, but that's the unfortunate truth.
2011 Microsoft MVP for Xbox!
debaser17 wrote:
Have you tried yourself? It's really very easy to open up a controller, all you need is a small screwdriver. Once you take the back off whats inside will generally hold together just fine. I would just take an alcohol swab and try to clean around the button as best i could, then pop the casing back together.
Yea, that is a wise suggestion as well. 
