Canker sores are essentially bacterial infections of the skin. You need to keep the area as clean as possible.
1- get some Ora-gel or something similar to numb the area.
2- brush your teeth as best you can with a whitening toothpaste. The peroxide in this will help sanitize the mouth. Gently brush the surface of the sore as well.
3- Rinse area with Listerine (has to be Listerine). You can also use Hydrogen Peroxide, but it tastes nasty
Do this 3-4 times a day, and I guarantee it'll be gone within a couple of days.