The Plateau is a comfort oriented hybrid with a very upright and set back riding position but so is a bike like a Raleigh Sports 3 speed... and I know people who have toured on these and laid down some pretty decent daily mileage and even taken them through the mountains.

You will probably be spending 5-6 hours in the saddle for both of these days so you will really need a decent saddle... am guessing it is not a race so maintaining a moderate pace should not be difficult if you are in shape and you remain comfortable on your bike.

I have ridden metrics on fixed gears, road bikes, and my touring bike and have even done this on a Raleigh 3 speed which was really comfortable but not the best bike to be riding when you had to deal with stiff headwinds.