Canadian Embassy is NOT issuing visa extension letters as of today, see their reply to my inquiry below:
(Admins, I am doing a new post for this so the info is easier to find Vs the reply thread I already posted on. Hope the duplication is okay)
TLDR : Answer Summary
As of now, the Canadian Embassy in Bangkok is not issuing letters for visa extensions, which were previously required to apply for a 30-day extension of stay in Thailand. It is important to note that even if other embassies do issue such letters, it does not guarantee acceptance by Thai immigration.