If you're looking to buy in Canada, try Great Northern Battery Systems down on Parkdale in Hamilton by the old steel mills.
GNBSystems Bought AGM battery sets from them a few years back and couldn't find a better price anywhere in Canada. Good customer service, too. They know about what they sell.
If you can wait until you travel south of the border, and depending on what you want/need, I'd try Sam's Club first, and then Costco. I've had good luck with batteries from Sam's Club (I live in a border town now). Have used their AGM dual purpose and AGM deep cycle (some branded as Duracell, made by East Penn Mfg) in my vehicles with no failures so far. After that, check West Marine's website. Sometimes their RV/Marine AGM/deep cycle batteries go on sale. Got a pair of GR27 dual purpose AGMs (deep cycle/starter also made by East Penn Mfg) for around C$300 on sale three years ago IIRC.
One more thing comes to mind. If you're only going to use 2 6V batteries connected in series to get the 12V to power your systems, keep in mind that if one cell in either battery fails, it takes the whole battery bank down. There is no redundancy, like there is if you use 2 12V batteries in parallel. You might sacrifice some aH going with 2 12V batteries, but if one cell fails in one battery, you may still have one working. Food for thought?