Emily-

You could ride the trail on either (assuming it hasn't been raining much), but I think you'd have a more pleasant time on the mountain bike. It rains enough up there that there's likely to be at least some mud on the trail. Plus, I've just found that larger wheels roll over stuff better (I love my Friday, but...) We usually do it with 1.5 slicks on my mountain bike and 32 conti top tourers on DH's hybrid, so it certainly can be done on something like the width you're considering.

Have fun - I doubt the leaves will be turning yet, but it should still be pretty up there.

CA