I bite the sides of my cheek, my tongue, my lip, etc. plenty enough... never gotten a canker sore. I did drink soft drinks, formerly, but haven't for many years. Didn't get them even when I did drink them, though.
I thought they were caused by a virus in the bloodstream. Are canker sores different from cold sores? Because I'm pretty sure that cold sores are caused by herpes simplex, besides diet cleanup, one way people treat that is by taking lots of l-lysine.