Some good advice here. Talk with your outfitter - they will recommend different brands to look at and also a pack size you will need. How much gear do you need to pack? How many days is your trip? All of these things will factor in to the pack size you will need. Try a few different brands and models out and see what fits you properly. Mystery Ranch is another for you to consider. With the amount of money this trip will cost be sure to invest in quality gear - especially boots and a pack. From what I hear about Alaska Dall hunts I would be sure to have good rain gear as well.
Sorry - I'm late on the post I see you have already purchased a pack.