Whatever bike you get it's probably going to get thrashed. So, don't spend any extra on "pretty". It probably won't be pretty when you get back. It may also get destroyed, stolen, or you may have to abandon it. Think about it bouncing around in the back of a pickup truck, stuffed in a trunk, or lashed to a logging truck.
26" wheels are stronger than 700c and you can fit much fatter tires. The fat tires cushion the ride and save wear and tear on you and your equipment. At times they may even be faster than 700c. You don't have to pick your way through rough conditions as much. You ride over things more confidently because you have more confidence in you wheels. Fat tires have more grip so the bike handles and brakes better. Fat tires float over dirt, gravel, and sand better. A 36 spoke 700c wheel is strong but a 36 spoke 26" wheel is even stronger.
If there's a lot of mud disk brakes may be nice. Mud accumulates around cantilevers. If you are constantly in wet conditions cantilever pads can wear out quickly and that awful grinding. I think the Shimano caliper is more robust than the Avid. I've used both and both brake well. I broke an Avid caliper putting on a brake cable. The threaded arm which holds on the caliper lever is made of a fragile cast material. It's easy to crack it if you are not careful and then the caliper lever falls off. Get a frame with both disk brake tabs and cantilever studs, you're ready for anything. Use rims that are compatible with rim brakes, don't use disk specific rims, and use disk brake hubs. Shimano has some new calipers that are compatible with road brake levers. Avid has had these for a while. Install auxiliary cyclocross levers for the really sketchy stuff. Shimano disk hubs use a center lock design making replacement rotors for them less common.
Look for some racks that mount to the cantilever studs. Brake screws are much more robust than water bottle cage screws. I'd bet they would not come loose. I think the skewer through the lower mounts has got to be way stronger than water bottle cage screws screwed into the dropouts. Chromoly racks have got to be stonger than aluminum. Racks that are welded together have no screws to come loose.
You are not going to be doing the fair weather, smooth road, close to civilization sort of touring. Almost any equipment holds up under those conditions and a bike store or help is a reasonable possibility.