A canker sore appears in your mouth and is an ulcer which is already basically open and there's no way to pop the canker sore.
A cold sore which appears on your lip or other part of the outside skin could be popped but it would be best to leave it as is and let it heal on it's own to avoid further infection.
You can get rid of a canker sore by using 1 tablespoon of baking soda and mix it with a 1/4 cup of warm water to rinse your mouth out with.
When you rinse your mouth with the baking soda and water the baking soda will kill bacteria as well as soothe the canker sore and the canker sore will eventually go away if you rinse your mouth out with the baking soda and water at least 2 times per day until the canker sore goes away.