Joshua has the power to threaten Foreman, but he just doesn't have the chin to last, Foreman stops him between the 7th and 12th round...
Joshua cowers under the Foreman gaze and goes down in three after trying to survive and hyperventilating.
I used to be convinced that AJ would wreck Foreman. But I now think AJ puts up a spirited effort and perhaps knocks him down. But George Foreman flattens AJ eventually. However, if AJ tries to cautiously box, he could outbox Foreman like he did Ruiz.
If AJ had the chin of Mercer or excellent defensive skills, I'd pick him every time. AJ hits hard enough to hurt Foreman and could very well drop him. He has a size and speed advantage. It's just his durability. When Foreman catches him, it's the beginning of the end. It's the same reason I was hesitant on picking AJ to beat Wilder (it's a shame that fight never happened).
AJ actually has the tools, size, and skills to win. The problem is that throughout his entire career, he not only doesn't react well to getting nailed by bombs, he has some of the worst survival skills I've seen for a man with his world class experience. Joshua just refuses to move his head for some reason and not one trainer has fixed this. He doesn't know how to clinch or even cover up properly. Doesn't always protect himself from body shots. Isn't very good at using his legs to retreat or fight backing up when hurt. My point being even if Joshua's doing good and hanging with Foreman, if and when he gets nailed with something big, he'll probably get stopped. Combine all these bad habits with Foreman's bloodthirsty and clinical finishing ability and you have a recipe for disaster more often than not outside of Joshua's proverbial puncher's chance. Unless Joshua fights the perfect fight and/or Foreman blows through his gas tank trying too hard to end things early, I'm guessing it's Foreman by KO within 5-6 rounds (but Foreman would have to endure a few bombs and may need to get off the floor at least once). It would be a good scrap while it lasts either way.
This would be the type of fight that gamblers could use to set themselves up for the year (or more). Foreman would beat Joshua. It's about as close to a sure thing in boxing as you'll get.