Rubbish - They want you to use them to get a bank account. OR so you can transfer the Fee for the Service to their bank account. Consider using another Agency and going to Cambodia and get the Visa Exemption 45 +30 (only 15 days less than the TR90, plus only takes one full day to do the Exemption border bounce).
Can't you open another account in Canada even with another bank, then you can get a back-up card. I use one card topped with low funds and have 2 back-ups. Also bring about $3-5k cash and just store in Hotel safe.
Most hotels do month to month. But no real website for this. Agoda does long stays and builds in monthly discounts, best is to ask Hotel when here. As as ruff guide monthly is half the rack rate. So, 800bht/nite would be around 12-14,000b/mth.