Usyk by comfortable UD
Bellew might win a few rounds by making it ugly and pushing the pace more than Gassiev but that's the best I think he can do...
For my money both Briedis and Gassiev, arguably the version of Glowacki Usyk fought too were better than Bellew and he beat all of them. Styles make fights though so I don't expect him to get shut down completely like Gassiev was, Bellew can punch in the fly more, he doesn't have to be perfectly set to throw punches like Gassiev, also I doubt his mentality would allow him to comfortably plod in the ring, staying conservative, even when he is way behind on the cards and it became obvious that he can't corner his man with shuffling forward step-by-step.
Bellew needs to take a page from Briedis' book though cause Usyk vs Briedis was mad close. I doubt he can reproduce that cause I think Briedis is better than him but he might be good to win some rounds.