I have done it on a road bike, no problem really, did run 25c tyres with a bit of extra protection. It is a bit bumpy in places, these can either be tip toe-d across or more effectively, ridden fast, paris roubaix style! I did it on one of the worst days ever, rain wise, so was looking to get home FAST!
Very boring route though, especially if you continue to Edinburgh, it ends up looking all the same. I think on a nice day with the sun on your back it could be quite nice, but anything but a lovely day it is pretty dullsville. Maybe a route that mixes up some canal path and some quite roads might make it more enjoyable?