Silly question, of course Wilder will win. if AJ fought Ngannou first and did what he did we wouldn’t have silly questions like this.
Wilder... Probably, not definitely. Ngannou would be aggressive and awkward - he could hit fairly hard, and Wilder wasn't the most durable. Stylistically it's probably not the best opponent for Wilder. At the same time, Ngannou was very hittable and Wilder despite the limitations should really be able to do it. We don't really know how good Ngannou was - he only fought two guys, one that proved he was levels above Wilder and another we can be fairly sure also was, and lost to both (just as Wilder would've)... But he has no wins, so we just don't know how good he actually was - we know he wasn't champion level, but that's about it. As a boxing fan, I would've wanted Wilder to win despite his limitations... In terms of what they've proven, you'd have to say Wilder, but I'm really not sure I'd have trusted him enough to bet on it.
I guess that's why Joshua picked Wilder to be his tuneup this summer for Fury, like Hearn said they would. Oh, wait, he didn't. They don't even think Joshua could slaughter a 40-year-old Wilder now ... five years removed from the third Fury fight! Wilder's still too dangerous a risk, as Hearn called him. You can stop kidding yourself any time.
I think Ngannou would win the mechanics of the fight, would look better, would push Wilder back and get better of the action, but thats not Wilders realm, Wilder does that while guaging and waiting for his right hand. Ngannou would look good and be winning the fight, and pre AJ I would have picked Ngannou to beat him, but after seeing AJs power effect him like that it makes it a 50/50 for me as Im not convinced Ngannou could take a prime or near prime Wilders power.