If you don't think you'll be touring much after this trip, you might want to consider a BOB trailer with your Trek. That way you can easily sell the BOB at not much loss when you're done with it and be left with a bike that you'll be happy with for other purposes. If you are planning to go loaded, you'll need your Trek with a triple and if you're in shape a standard road triple is doable. Your lowest gear combo with a triple would be 30/26 (30 gear inches) again doable if you don't take the kitchen sink.

+What Zona Tandem said. You'll need to practice centuries before you take your tour. But I'm not sure if the marathon analogy is accurate, because 10 hours on the bike at 10 mph puts alot less stress on the body than 4 hours (or whatever) running 6.5 mph.