Hi Turquoise, your partner is British and you are Canadian. So let's look at what needs to be done in order for the two of you to get married in Thailand. Because quite understandably Thai law does specify some requirements.
Your British partner!
This page (click) is very helpful and describes what needs to be done. Thai law requires a non-Thai person wishing to marry in Thailand to sign an affirmation ... at their embassy in Thailand. It is not possible for the affirmation document to be signed anywhere else, because when the affirmation is checked by the Thai Ministry of Foreign Affairs they do check that the countersignatory from the embassy is on their pre-approved list.
So for a British person the procedure is clear, and fully described on that webpage. There are even samples of affirmation documents. Your partner's own affirmation document should be prepared before leaving for Thailand.
He is waiting for his divorce to come through. So an
original (not a photocopy) document needs to be attached .... the Decree Absolute ... and that
must bear the red stamp seal from the Court.
You, Canadian! You will need to go to the Canadian embassy in Bangkok.
Click here for an informative webpage.
For British Citizens it is merely a question of going in one day, signing the document, then returning the next day to pick up the countersigned document. For Canadian citizens the website mentions "one morning".
After the affirmation documents have been signed, get them translated into Thai, and then take them along to the Thai Ministry of Foreign Affairs, as mentioned on the British Embassy website. After the Ministry stamp has been applied, you can simply go along to an Amphur (Register Office) and register the marriage. No appointment is needed.
However as neither of you speak Thai (I presume) you really will want to take along someone to help you, and for a fee the translation bureau, of which there are many in Bangkok, will be only too happy to oblige.
The procedure to actually register the marriage? Very simple indeed ... and form-filling exercise ... hand over documents ... Ministry-stamped affirmations and passports .... pay a small fee ..... wait a few minutes ... then get handed your marriage certificate. Do ensure that you get the translation bureau to translate that certificate from Thai into English as their final service to you.
In all of this ... no mention of a religious ceremony! No, in Thailand a "mere" religious ceremony is not a legal marriage. If you also want a religious ceremony that is something else entirely and nothing at all to do with getting legally married.
To summarise .... you could easily be married within 4 or 5 business days of arriving in Thailand.