I would lean towards Povetkin; the Lerena fight gave a glimpse as to how Dubois would deal with shorter, compact-punching, heavyhitting fighters like Povetkin, and what we saw doesn't bode well for Dubois. The only difference between Povetkin and Lerena is that Povetkin is orthodox, but in most other facets he is better.
Would be a total shootout. Dubois has the physical tools to get to the punch first but Povetkin is more skilled and unpredictable. Barely going with Povetkin by KO, but not confident and my opinion could change.
Tough fight for Povetkin as Dubious is much bigger and Povetkin isn't as fast or rangy as Usyk. So Povetkin is going to have to mix it up at close range which is dangerous. It's obvious Povetkin is more skilled and mentally tougher but if he can't get Dubious out of there and eats some nasty ones he might lose. I guess I would back Povetkin to outlast him and TKO him in the later rounds. Povetkin was pretty hard to KO back in the day, people forget that. He wasn't getting KO'd by jabs and sore eye sockets. Wlad dropped and rocked him multiple times and he lasted 12 which was rare at the time against Wlad.
Povetkin would have too much for Dubois, he was extremely durable and was only not champion because Waldo hugged the living death out of him. If that fight had been fought according to basic boxing rules, Povetkin gets the W.
Head to heads have to prime for prime or we might think Pov is a guy who gets into life and death wars with limited fighters like Huck, shaken to his bones by big Pricey and stopped by the limited but entertaining Whyte...and he is way, way better than that.