First of all they didn't close your account, they froze it.
Second, they did it to everyone, even people that already verified their information. Multiple reports of people that went in and provided everything then frozen again the next week. They had to go in and show everything again.
Do you already have a Thai bank account? If not, you need to apply for a non-O visa in Canada, and then that visa will allow you to open the required bank account in Thailand that you'll need to apply for the extension.
If you already have a Thai bank account, you can travel to Thailand as a tourist and then apply for the visa in Thailand, but it's still much better to apply in Canada. It'll save you at least 2 trips to immigration, and a lot of time and effort.
Note that if your marriage is not already registered in Thailand, you'll need to get your marriage certificate authenticated by the Thai embassy in Canada before you leave so that you can register your marriage in Thailand.
You won't be applying for a retirement visa in Thailand, because you'll already have the retirement visa from the embassy. You'll be applying for an extension in Thailand.
Traveling to Thailand on a non-immigrant visa does not have any requirements for onward travel as this type of visa can be used to establish living in Thailand.
There's no such thing as going to an embassy anymore. Your application will still be processed by a Thai embassy in India, but it will all be done online.
Normally can be used, depending on your immigration office. But there is a distinct risk in using an account like this, as the exchange rate can fluctuate bringing you out of compliance with your visa requirements.