You know I can remember back in 2008 or so when Hopkins fought white American Kelly Pavlik. At that time, Pavlik was an undefeated knockout artist and looked unstoppable (similar to how Kovalev is viewed today). Mpst boxing fans, myself included thought Pavlik would win by KO but we were proven wrong when Bernard boxed brilliantly and seemed to win every round. Pavlik struggled to land anything all night and never got going.
So, this is a very risky fight for Sergey. Bernard is never an easy fight and even when he has lost, its usually been to speedy or volume-punching based fighters like Joe Calzaghe. If Bernard does have a weakness its his lack of punching output (Bernard often throws only 30 punches a round) and at times Bernard can be a bit slow. Therefore it is crucial that Sergey throws many punches, lets his hands go, and dictates a fast pace.
Fortunately, I think Sergey is better than Pavlik in terms of defense, speed, and he hits harder, so it should definitely be a closer fight. Obviously, with Sergey's power he can literally end the fight with a single shot.
This is a real test for Sergey. We know he hits hard but agaonst Hopkins we'll see how good his accuracy, defense, and movement is.
If Sergey lets his hands go often I think he beats Bernard.