Can Canadian citizens enter Thailand without a visa or do they need to apply for an e-visa?

Yes Canadians can come in 30days visa exempt.

Just need Thailand pass, which will likely be scrapped doon.

If you show up with a Canadian passport and no visa, you'll be stamped in for 30 days visa exempt.

You're still going to need a ticket out of Thailand within 30 days or your airline likely won't let you board your flight.

Also immigration can ask you to show 20,000₿ or equivalent in a different currency, but it's rare and usually reserved for people they want to deny entry to.