Can a Canadian expat switch to a multi-entry tourist visa after entering Thailand on a visa-exempt status?

Just FYI. RTE Ottawa says clearly this.

Happens quite a lot that people apply for visas online but don't get it issued before they fly here.

Sadly they can't activate the visa once their in thailand, BUT as people posted, they can exit/re-enter, show the PDF print out when they re-enter and get stamped in on the visa that way. They can do it by air or land, no issues at all

Since they needed to show a need for the METV, ie travel itinerary to another country, they can activate the METV when they return to Thailand.

Btw, when did they apply? Vancouver or Toronto?

Exit Thailand then come back - from CNX fly or the Lao border in Chiang Rai.

Yes, they would just have to pop out of Thailand and then enter with the metv