I too feel Kessler could win this fight. In recent fights (which haven't been all that numerous) Hopkins has seemed to age in front of our eyes.
At this advanced age he is relying on guile, expierience and in the case of the Wright fight questionable tactics in order to obtain victory.

In order to attempt to beat Kessler Hopkins would have to raise his work rate considerably. At this advanced stage of his career that would be betrimental and we would surely see him tire.
Hopkins, has been holding increasingly in recent times. Against the younger, fresher and in my opinion stronger Kessler, he would not enjoy the same advantage that he did over Wright. He would find himself bullied and in close with a fighter who can bully as much as Hopkins can.
Kessler would make active attempts to keep Hopkins on the outside, where he fires his most dangerous punches, he is possessed of good movement so it isn't unfair to say he could unload a lot of punches on Bernard.

I f the fight happened five years ago I'd say Hopkins, but today Kessler has the edge.