The idea that Germany and Russia could avoid conflict is unlikely at best, Mein Kampf was a long rambling diatribe about the Jews and Communists where he lays out his plans for both, from the time he gained a speaking platform he repeated the same themes of living space in the east over and over.
I also doubt that the declaration of war with the US would have changed anything, American servicemen were already being killed in Uboats attacks in the Altantic escorting convoys to Britain, my guess is that once the US became involved in a war Germany was going to be the first target.
Perhaps a better question would be what if Japan hadn't attacked Pearl Harbor but instead focused on British possessions in the Pacific and Indian ocean, would that have kept the US out of the war?