I tend to get canker sores when I eat too much sugar or if I eat corn syrup at all. I recently went on vacation, ate out a lot, and inevitably got a sore. This one was worse than usual and progressively worsened over the course of a week.
When I returned from vacation and ceased any excessive sugar intake I decided to try treating it with baking soda. I applied a small amount of baking soda directly to the sore in the morning. Twice throughout the day after eating I mixed baking soda with water and rinsed out my mouth. Before bed, I applied baking soda to the sore again. The last application caused it to start bleeding! By the next morning my sore looked more inflamed than before and I even had another one forming!
Needless to say, it didn't work for me. I hope others have better luck with it.