Lay off, guys, it's a NOOBWI
Total ASB, and here's why:
Hitler spelled out in Mein Kampf that he believed Germany's destiny was to colonize the western USSR and establish hegemony over the Slavic peoples of Europe. Since much of the USSR was Slavic, this all but rules out an alliance.
Another thing he called for was the destruction of Bolshevism. In case you didn't know that means the USSR.
Nazism and Communism are dialectically opposed to one another. One preaches racial equality, the other racial domination. They could never work together.
You could also argue that Stalin was even planning to invade Germany, and maybe he was. If so, this is another reason why it couldn't work.
And then you forgot the small fact that..........
American capitalism is opposed to both Nazism and Communism, so having the USA ally with both of its mortal enemies is, in itself, it enough to break the deal.
Not to mention the fact that the US was helping the British via Lend/lease, so it'd take a little more than "no pearl harbor" to bring America to the side of the Axis.
You are right about one thing though- an American/Nazi/Soviet alliance would have made for a bad day in Britain.