I see on https://ottawa.thaiembassy.org/en/page/visa?menu=5f213a85e65dbd7eb1463d9a that you have to use the eVisa application on thaievisa.go.th
During this application process, you will come to a page with the following:
When I made this application, from Switzerland two months ago, under point 6 "Proof of accomodation in Thailand" I uploaded copies of an invitation letter from my wife and of the house registration book for the residence listing my wife as a member of that household.