Carnera UD or mid round KO.He would jab and move around in his clumsy way to avoid some of Jess's punches.He would also smother a lot of Willard's punches.His good hand and body speed is also better than Jess's.OPrimo all the way here.
Although Carnera was superior as a boxer, and had more of the rudiments of the sport down, let's say than Willard, I've always thought that Willard would outlast and wear down the Italian for a late round stoppage. Willard could take a punch better.
Willard lost 3 fights inside the distance once when he was green and quit .Once when he was nearly 38 fat and complacent ,and Dempsey had to half kill him to stop him,and once when he was nearly 42 against Firpo ,after doing well his legs gave out.What makes you think that Carnera could stop him?
If Willard just lets his hands go, he should be able to bomb out Carnera the way Baer did. Carnera does has underrated boxing ability, but I don't see what he could do to hold Willard off if Willard makes a determined effort, and he's shown a suspect chin against smaller/lesser punchers than Willard (heck, even Tommy Loughran wobbled him).