I've recently notorized documents as a Canadian in Tokyo (not for the DTV) - you shouldn't need to go to the embassy, you should be able to just go to a regular notary in Tokyo unless the Thai embassy needs you to do it in Canada for some reason? I would confirm with them.
correct we were tourists, I emailed their office ahead of time to make sure we were able to apply there. I emailed a few embassies and most accepted tourists but Singapore told me only residents were able to apply there.