Someone with a much more aggressive international policy then Stalin in charge who starts attacking states in Eastern Europe before Hitler can start meddling around. Trotsky may fit the bill, although he faced an up-hill battle since he had made political enemies out of practically everyone who wasn't Lenin. His idea of turning the Red Army into one big workers militia also would probably be counter-productive and not make it much of a war. You might be able to find some other contenders with a better shot at power and a more realistic idea of how to shape the Soviet military and industry...