they would've came over here and made us all slaves
Ok, I can officially say that this is educational propaganda.
Germany and Japan could barely keep the war up when they were winning, in fact Japan was much more aware of their limitations then Germany was, there is no way either of them would have crossed the ocean to take on the United States and Canada.
I can understand why you think this way. History of World War II is taught in such a way that the allies seemed like the underdog, rather then the other way around, where the Axis were evil supermen.
The fact of the matter is that really while they shot under par doing much better then anyone could have predicted... They didn't have the ability to hold domain over the lands they took, and their own institutions were bleeding them out all on their own.
In fact it is doubtful the USA's involvement in World War II would have changed the outcome other then Russia's counter attack and altering the beliefs of Japan.
IF Germany took over Europe, they would have lost Europe.
Heck while Pearl Harbor was actually rather pointless in the grand scheme of things, ignoring that it was a catalyst to involve America sooner. That was why America was caught by surprise. Better yet Japan had to expand a lot of resources to do it.