I use a Wenaha pack for my Australian Shepherd. It has a saddle with a harness that has padding where the buckles might rub. The pack bags are held on the saddle with Velcro strips, so you can remove the pack and leave the saddle on breaks, stream crossings, etc.
It is made of heavier Cordura and I recommend that, as the dog brushes up against rocks and logs and gives the pack a pretty good beating. It takes a while for them to learn to gauge the extra width of the pack too.
My dog likes the pack and it is a sign he is going out, so there is a positive association with it. He knows his treats are kept in there too, adding to the positive association. He doesn't carry much– a little water, food, p**p bags (he carries it out too), and treats. I use an old Sierra Cup for a water dish and food bowl. He seems to think it is "special" — getting to eat out of a "people" dish. Get the pack out and he's doing back flips.
It needs to be loaded evenly and the load should be on his shoulders. The straps will need to be snug, but not too tight. Don't get a pack with huge bags– fit is as important as your own pack gear.
I like the look of the Granite Gear packs, but haven't tried one. They are compact and neat and the harnesses look good.
Please be a good neighbor and keep your dog on a lead on the trail. Not everyone loves dogs and some have dogs with them that are unruly. Some people are just plain scared or annoyed with dogs. You will know the dog lovers on the trail. I've been working on light leads and experimenting with lengths. I have let him off lead when no one is around, but it gets to be a pain if there is sporadic traffic on the trail and I have to stop and get his lead out. I usually tuck the lead into the pack for times like this. Ruff Wear makes a short lead with Velco tabs, so it stows like a collar and deploys with a tug.