How long can I stay in Koh Samui as a Canadian citizen and what are my visa options?

If you have a Canadian passport then you cannot get Visa on arrival as that's only for a few countries.

As a Canadian you would qualify for visa exempt, which is not a visa. It is a 30 day entry stamp into Thailand. You can also apply one time for a 30 day extension, giving you 60 days in total.

If you want to find out about education visas then find a school you are interested in and ask them. Most of the schools on the islands charge very high fees for visas (10,000+) on top of the class fees.