Before you send it - go to the CanonUSA site and file a repair ticket with them online. Explain what you would like to have done. They will send you a repair number and tell you what to include in with your camera(or lens or whatever - usually a bill of sale).
Then you go to the UPS store. Take the camera in its original box, if possible (taping your repair number to the box - it doesn't hurt to use an adhesive label on the camera also).
You will be insuring the camera for its value, so UPS will insist on packing it for you. Let them. They will give you a tracking number, and off it goes.
I did this with a lens recently - it took ten business days from the date they received it. Sometimes I've had it take less; it depends on what all is going on. But by filing for a repair number, you will find you're already in the system, rather than waiting for it to be processed when they receive it.
After they get it, they will email you with an estimate (or tell you if it's covered under warranty). You then okay it (I use the telephone number rather than the web-site), pay for it by credit card (if possible) and they fix it and let you know when it has been shipped back. You will need to sign for it upon its return.