On December 6, 1941 the vast majority of Americans didn’t want to get in another war in Europe.
If Japan hadn’t bombed Pearl Harbor it wouldn’t have galvanized American support for war. Even then, Hitler could have avoided America joining the European war by just declaring that Japan did that on their own and not joined in declaring war on America.
Declaring war on America and attacking the USSR while leaving Britain unconquered were Hitler’s two biggest blunders.
Even if Hitler didn’t declare war on the US, it only would have been a matter of days or weeks before a U-Boat sank a US ship supplying Britain, which would have provided us with the Casus Belli for declaring war on Germany.