I disagree with the Soviet part. Operation Barbarossa did in some part succeed but Hitler’s SS so antagonized the Russian people that they began to fight the Nazis in a truly vicious partisan way.
I think what would have happened is that the Soviets and the Nazis would have beat themselves to death on the Russian steppes and there would have been no iron curtain.
We would have beaten the Japanese in Asia, and started the desert campaigns across North Africa into Italy just as we did.
It would have been more difficult, but we would have eventually won against them.
The heavy water experiments would have succeeded as Britain will not have knocked them out; will we have perfected our uranium bombs before Germany could have brought their nukes to use against us?
The German Army also bears responsibility for antagonizing the Russian people. The SS were not the only forces brutalizing the population of the USSR.
We got lucky that our German scientists were better than Russia’s German scientists.
With Britain subdued in 1940 it's likely Roosevelt would not have run for a third term since effectively the war would have been "over". Remember in 1940 Germany and the USSR were still "allies" and the American pacifist movement was dominant. It was only because of the Battle of Britain that Roosevelt was able to push through lend-lease or re-institute the draft. Without this impetus America would have slumbered on as Hitler consolidated his hold on all of Europe.
Britain's capitulation would also have given Japan a free hand in Asia, giving them needed access to resources. With a pacifist US there may have been no need for Pearl Harbor.