Since I have picked 2 outside MSR winners (Ciolek and Goss), I'll chime in
It's gonna be wet and crap weather which will drain the energy of the race and lead to a lack of cohesion (crashes) which will make the race difficult to control. So knowing that, I think you can strike Cavendish and Greipel straight out.
So let's look at sprinters who have been climbing well lately, I think Degenkolb is probably the best of the lot. He's also won long classics with a sprint at the end (Paris Tours, even after going on the attack before the finale) and he's got the body composition to go well in the wet. Of the headline names, I think he's the best bet vs his odds. Sagan is 4.6-4.8 to 1, decimal odds, pretty fair really, but in a wet one, anything can happen in a split second. Senimentally, I'm actually rooting for him, but I wouldn't bet on him at those odds. He's been good this spring, but not as good as the last one.
Outsiders, Sprinters- Arnaud Demare is my pick. He has made a really nice progression over the past few years and he is fairly handy up the hills as well. He wouldn't be forced to work in a small group like Sagan or Cancellara. My only question is does he have a mental strength to be a real killer and refuse to work like Gerrans did. I'm tempted by Modolo as well, but I doubt he has the grinta to tough it out in the cold and wet. Mathews was actually climbing the best of all the sprinters in Paris-Nice, but then had to abandon with saddle sores which is too bad. I don't know his status for MSR.
Outsiders, Puncheurs- I'm definitely throwing a few quid at Ulissi as he's 30-1 and been fantastic so far this year. Stybar has quietly been goingn very well lately.
edit- no Kwiatkowski or Bentacur
p.s. if you want a real shot from the blue, Ponzi's been riding well too.