Which is the best and fastest way to get rid of a canker sore?

Cauterization ...: ... Seems to bring the fastest resolution to canker sores. Though inconvenient, treatment of a canker sore with a carbon dioxide laser (many oral surgeons have these) can result in almost immediate relief of pain but complete resolution will still take a while. Local compounding pharmacies also have custom topical products that work well for canker sores.

Canker sore relief: There are numerous over the counter medications to help relieve discomfort from canker sores. Some things you can do to help speed up the healing time is to rinse with warm salt water, suck on Tums (calcium carbonate) throughout the day and avoid acidic foods like nuts, vinegar dressings, orange juice and tomato sauces.