I wouldn't throw 100lbs in right off the bat, but I would add weight as the season gets closer. Doing some "real world" backpack weight training has been the key for me!
4-6 miles with 45-60 lbs 2 times a week
80 lbs intervals (hill training/short distance)
60 lb ascent lunges
40 lbs at 4 mph for 8-10 miles
I usually do 1 heavy day a week (80+lbs), but will occasionally exceed 100 if I'm feeling good. I would say that your upper end training # is going to depend on what you plan on carrying during the hunt.
If you think 120lb pack loads are in the cards, than I would at least do a dry run with that weight and see how it feels. I know that I hit loads that exceed the 100 lb range, so I will train with that amount, but I wouldn't suggest that unless you feel comfortable with that amount.