I don't have a direct answer for your question about visiting Thailand from Canada on an RTD, as I've never done that specific visa myself. But I did take a look at the Thai embassy website for travel info from Canada, and it mentions some long term visa options there:
https://www.thaiembassy.com/travel-to-thailand/travel-to-thailand-from-canada
My guess is they'd want to see your RTD card, proof of onward travel, and funds as the other person said. The embassy site might have a checklist of exactly what's needed. I'd check there first or give them a call if you can't find all the details online.