What is the quickest way to make a canker sore heal and what can be done to prevent canker sores from forming?

These are not viral infections. There is no problem with trying a mouthwash. I have seen success with maalox mouth washes. A prescription for corticosteroid gel designed for mouth use does good work. In my experience the cause of canker sores is elusive. Stress may play a role. If they don't heal after a week see your physician, dentist or an oral surgeon for evaluation & advice.

Over the counter gels or liquids applied to viral lesion will help. The lesion lasts about 5-7 days. In future reduce anxiety, stress and eat and drink those foods and liquids that have a low acid content. Too much fruit juices and lemons are a cause.