If we were going to flip the Soviets from allies into enemies overnight, we would have needed the support of the Japanese, to keep the Soviet Army from moving from the Manchurian and Mongolian borders to the European theater. The Japanese, having seen how the Americans handled conquered people, and also knowing that the Americans were not going to be conquered in a final battle, could have decided on an armistice that would have allowed them to retain Manchukuo, Korea, and Formosa, give up the Philippines, Indochina, Burma, Jehol, and southern China, and concentrate its forces, buttressed by American supplies and materiel, on Mao’s forces in NW China, and the Soviets in what would become its eastern front. It would also free up the Manhattan Project to drop its nukes on the USSR, with the first two landing on industrial centers, and the third, if necessary, hitting the Kremlin, just as in actuality the first two hit remaining centers in Japan, with the third planned for Chiyoda-ku, obliterating the Imperial Palace.
The result in Asia would have been an Imperial “Greater Japan” allied with the US, Britain, and a nationalist China, a post-communist Russia, and a 1939-border Europe with democracies throughout. Moreover, without a Second World to compete with the First World, the history of the Third World would have been very different, but how that difference would have shown itself is, I think, unknowable.
As I understand it a great deal of the Soviet army was moved from the Far East/Siberia to the Western front during the war. The Japanese were surprised how quickly Stalin got them back in the closing days of the war. As an aside the U.S. Navy would have quickly turned the Baltic into an Allied lake. Creating opportunities for multiple landings and fronts.
Stalin stripped Siberia of it troops after December 7, 1941, when he knew that the Japanese would not be attacking in Manchuria. Those troops ended up being used for the late December, 1941 and January 1942 offensive to drive the Germans from Moscow. The forces Stalin used to attack in Manchuria in August & September 1945, had been shipped there from Europe.