Are there any homeopathic suggestions for drying out an open canker sore?

OTC medications. Canker sore or cold sore? You can't dry out canker sores in the mouth. Most drug stores have numerous otc medications to help canker sores feel better while they heal. It's probably worth the visit than to try anything at home, especially if you tend to get them often. Ask your pharmacist which one he\she recommends. For cold sore, ask your dentist for mx.
Baking soda. I have found you can rinse with baking soda. It is palliative treatment. The canker sore may not actually go away any sooner, but you should be more comfortable. You can also take sodium bicarbonate to create a more neutral ph. Check with your doctor to be sure the sodium bicarbonate is ok for you to take.