Can I extend my visa exempt stay in Thailand for an additional 30 days while in the country, and is it better to get a tourist visa before traveling from Canada?

Applying in Canada for the Thailand multi entry tourist evisa is definitely a great way to go. You can stay in Thailand for 60 days, visit Vietnam (or wherever), re-enter Thailand for another 60 days, and then repeat if desired for 6 months (or the date of evisa expiration).

If you decide on visa exempt, all the airlines flying from Canada will ask for proof of onward travel at the 30 day mark. We've flown from YYC, YVR, YWG and have been asked by Air Canada and any of the Star Alliance member airlines.

If you travel to Thailand without a visa, you'll be stamped in for 30 days (this is called visa exempt) and you can apply one time for a 30 day extension at your local immigration office in Thailand.

You also have the option of applying for a tourist e-visa before you travel to Thailand. With this you will be stamped in for 60 days, and can apply one time for a 30 day extension.

If you're not planning on traveling around SE Asia, I would apply for the tourist visa before you leave for Thailand. The e-visa system is completely online and you don't have to send your passport in anymore. You get a pdf e-mailed to you and print it out and that is your visa.

If you do this you can get 90 days, and then go to Vietnam and return and get 30+30 days which should cover you for 5 months. If you do 30+30, 30+30, you might still have to do another border bounce to reach the amount of time you listed.

But if you are planning on traveling around SE Asia while you're here, then the visa exempt entry is probably best since you'll get 30 days every time you enter Thailand.