If your bike will take a 700 x 40 I would go with the Marathon Extreme. I have toured with the 26 x 2 version, both on pavement and gravel and I love the tire. It rolls remarkably well on paved roads but gives great traction on the rough stuff.
I have done 1800 kms through Mexico on mine and just did some crazy sand roads on them this weekend.
Enjoy your trip.