You can't hurt what you can't punch. Louis is too slick and smart to get caught by Wilder. Louis wins by late stoppage.
About the only thing I’ll give wilder is that he had enough power to knock out just about anyone. That and a pretty good chin and fighting heart. But Louis would tear him up on the inside, especially given that wilder isn’t great at taking advantage of his reach
Louis walks Wilder down and takes away his reach with short crisp combinations up close. Wilder can't fight backing up, has leaky defense, and can't even clinch properly. Terrible inside game. Wilders only chance would be to time Louis on his way in with the perfect right hand down the middle. I could see Wilder scoring a flash knockdown, but then getting picked apart by Louis who takes away Wilders reach advantage with subtle parries, counters, all while operating behind a stinging jab. Louis by KO within 8-10 rounds. If this was peak Wilder vs Louis of the 1st Schmeling fight, I'd give Wilder a decent punchers chance (assuming he actually listens to his corner and tried to follow the Schmeling plan). That would be a very dangerous fight for an inexperienced Louis.
I somehow don't think Wilder could replicate Schmeling's technical brilliance and timing. Many actually skilled fighters tried to replicate Schmeling's success and they just couldn't do it.
Watch the 2nd Ortiz fight. Wilder waited the entire match to set up that nuclear right hand. I would still favor Louis to win, but Wilder has a significant chance against a less experienced Louis who was weak to right hands leads.
If Joe Louis knew who he was fighting (if Joe watched some of Wilder's fights), Wilder would be knocked out. Louis is more skilled, has a higher ring IQ, and Joe Louis is a mechanical marvel. If Joe entered the ring without knowing who his opponent was; Wilder would have a puncher's chance from distance.