What is the best way to transfer my Non-O visa to a new passport while in Thailand?

You can transfer your Non-O visa stamp to a new passport either in Thailand or after renewing it in Canada. If you renew your passport in Thailand, you can take both passports to the immigration office to have the stamps transferred. Alternatively, if you renew in Canada, you can show both passports at passport control when entering Thailand, and the immigration office can also move the relevant stamps then. It's important to note that if you renew at your embassy, they may make your old passport unusable, regardless of the location you choose.