"Would the main pack body for the Ohm or MP+ hold a tent, sleeping bag, bear cannister, small amount of clothing and rain gear?"
A lot would depend on how big a tent, how much food, and how big a bear canister. I trial packed my Ohm with 8 days of food in an Ursack(with insert), plus all my other gear, with plenty of room to spare. Caveat: I store my raingear in the front mesh pocket where I can get at it quickly and my Rainbow gets strapped to the top when I am using a tent because I don't like removing the strut. Still, if you have something like a Contrail, you should be able to get it in the pack, unless you are using a monster canister like a Garcia or Bearikade Expedition. I can't comment on larger diameter canisters, but my sense from packing the Ursack(8" in diameter x 12" high) is that a Bearikade Weekender(9" x 10") should fit just fine and leave even more room for a small tent.
Anyone out there with experience packing a Weekender into an Ohm to confirm or deny my sense of it?