As long as you have the financial requirements (800k baht in a Thai bank account or monthly income of at least 65k baht) there should be no remarkable difference among the 2 nationalities
If anything else fails, go and book a hotel room for one night. Ask the staff to hand you the tm30 report slip. You need tm30 only for extensions of visa and 90 days report anyway.
Looks like multi entry non O is your best option. It's valid for one year but you have to do a border run every 90 days. No financial proof required. You can go apply in Savannaket or Ho Chi Minh
Update, you make sure you have a cheap outbound flight booked (e.g BKK to Siem Reap). Check in staff at departure still may want to see you will exit from the kingdom within 30 days. Of course you will not use it, but book it before you leave Canada.