For what you are looking for, I would look for something along the lines of the GSPs, hard thing is that NONE of the dogs should be going on such long walks/hikes until they are at least 18-24 months old when the growth plates close, so keep that in mind.
Larger breeds like the labs, shepherds and mountain dogs are prone to having back hip/joint/back issues, and such vigorous exercise might exacerbate thoughs.
You also need to consider the type of climate that you live in, and remember that a lot of the dogs that might be considered usually have very high prey drive, so having on a long lead vs off leash might be prefered.
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