I would pick Kessler, this is something that needs to happen. I'm sure Mikkel is itching to get at this southpaw.
Have always thought Kessler would be too good for Bute, and would probably win easier than many think. Both have good workrates, but Kessler would beat him to the punch more, and give Bute trouble with his crisper combo's. Kessler fairly wide UD for me, with a chance at stopping him late.
Kessler by late KO but Bute would be about even on points at that the time of stoppage. would be a great style match up.