How far in advance should a Canadian apply for a 60-day tourist visa to Thailand?

Better to just arrive and get 30 days visa exempt then go to immigration on final day (verify immigration holiday dates) and get 30 day extension. Much easier and no pre-planning involved (other than spending a few hours to complete extension step).

It took me about 3 months to get 6 month multi entry visa since new post covid e system was established..(additional info on several issues was requested, mainly financial). I had six visas prior to that which involved just sending passport in to local Canadian center and getting it back within two weeks..As a result, flight time came and I entered under visa exempt, only to finally receive the multi entry about 3 weeks after arrival..I kept local Immigration notified, and initiated multi entry at a Laos crossing. Remember the only proof you have is the attachment sent by email when visa is finally approved and you need that each time you do your 60 day bounce, since all that appears in your passport is regular entry stamp , not full page "plate" type used in the past.

Canada is slow. Embassy website says 20 business days, mine took 6 weeks.

You have 3 months to use the visa once it’s issued so once you’re inside that timeframe you might as well apply.

Different Embassies/Consulates have different turn around times. Here in the U.K. it’s usually very quick but I don’t know about Canada.

Maybe apply in the middle of April. Most Visa will be valid for 3 months from the date of issue. You must enter Thailand within the validity of the visa which would be latest by midd Juli.