honestly about any bike will work, so find one you like. If the trail is crushed stone, like many in our area you likely want to stay away from really skinny road tires. But, laws of physics will prevail, so the lighter the rotating parts (wheels, tires, etc.) the further and faster you can ride using the same amount of energy.
My trail bike is an old Trek, with 28mm road tires on it. They are slightly on the skinny side, but have ridden them on soft rain soaked trails without problem. A 50 mile day even for someone out of shape like me is not a huge problem.
My wife wanted something very comfy, so we bought an Electra Townie for the geometry (almost no weight on hands, flat foot stops). Then swapped the wheels for some strong but reasonably light road wheels, and lightweight 32mm wide tires. Also swapped on some better shifting while we were at it. It works very well on rail trails.
I know many recommend mountain bikes for rail trails. The function great, but you give up some speed and distance do to the heavier components. But if you don't plan on riding long distances, they should work just fine.