I use the Exos 48 most of the time, and one of the things I like about it is that it is an unadorned "bloody big single sack" (as Colin Fletcher used to put it.) I also have an Atmos 50, which has a divider between compartments, and I believe I can put more gear into the Exos 48 simply because the pack bag is simpler, and things fit better for some reason. It also seems to be slightly "rounder."

The Exos 48 won't hold the canister, obviously - I just wanted to tell you about it because the Exos 58 is also a single large main compartment, and might work.