In reply to jonathan watt:
I did a ride in that area with my two sons last summer, quick scoot around Guernsey and Jersey, over to St Malo, Mont Saint Michel, Avaranches, Coutances, St Mere Eglise, then down all of the D-Day beaches to Caen. We took 5 days so as we could visit all of the beaches and museums as well as Mont Saint Michel.
We used quiet roads all of the way and they were brilliant, fairly quiet and felt safe (late June). The only day that we encountered more hills than expected was the Avranche to St Mere Eglise, but I guess you'll stay south of that line.
The one thing that can catch you out is wind! To clarify, a lot of the area along the coast is pretty exposed, we thought we'd be fine, expecting a westerly or south westerly and instead got a constant easterly, it certainly made a difference and we took turns at the front.
IMO if you're going there you might as well make the most of it and visit some of the great sites, including Bayeux, especially as it's not the cheapest, or shortest, ferry ride to get there.
I've not got any GPX files and anyway you'll likely be on a different line to us, but plotting them on a free mapping site won't take long and will give you the distances, elevations etc.
And when you get back you'll be able to watch the 2016 TdF setting off from Mont Saint Michel.