I would stay away from longhaired dogs unless you enjoy picking cockleburs out of a thick coat. Personally I like German Shorthairs. The trick is to find one that isn’t too wound up.
Conditioning: Feet & Aerobically
To do that kind of mileage you will have to condition the dog aerobically and really toughen up the dog’s feet. You can’t just take a dog that is used to carpet and grass out on a trail and not expect to have problems. Running around a grassy yard will soften up the pads leading to a very painful experience for the dog when the pads come off, and a heart wrenching one for you when you realized it is your fault because you didn’t condition the dog’s feet properly. Think about walking on a gravel road with your own bare feet and you’ll see what I mean. Begin to work the dog’s pads up by having the dog take short walks (less than a block) on a concrete sidewalk once a day. Once the feet are toughened up a bit make it a full block, then two blocks, and so on. If the dog is licking their feet you have gone too far.
Work the Dog: Voice & Whistle Commands
Your dog should also be very disciplined when it comes to voice and whistle commands. My dad lost a dog for three or four days because his dog was so poorly trained. They were in the woods, a deer took off, and so did the dog.
So you have to work with the dog on voice and whistle commands. Working with the dog doesn’t mean twice a year, every once in a while, or once a month. It needs to be regular and often. Once or twice a day at first, and then two or three times a week once the dog is trained. Dogs have a knack for finding skunks, porcupines, and rattle snakes so the commands will help with that.
Rest
You will also need to make sure your dog is drinking, eating, and resting enough. Dogs generally don’t stay on a path like a human, at least the one’s I’ve been around. They run here, there, and everywhere. Exploring everything that smells interesting. Out in front of you and then back, to the left of you and then to the right. So a 10-mile hike for you is a lot longer for them.
One other thing… My dad has had four German Shorthairs. Two with pretty much a solid chocolate colored body (like the head in the above link), and two with a speckled body. The solid body dogs had a much longer lifespan (16 and 17 years). And the male chocolate body dog we brought home from the pound was the smartest, well-tempered, disciplined, affectionate dog I’ve been around. Even though his previous owners starved and abused him.