well.. 1 stalin wasn't exactly the gung ho lets invade the world type, he was content with his empire and consolidating his power. so you will need a different Stalin or a present danger threat.
2. Mussolini wasn't exactly a communist, nor a great friend of them the better he got to know them.
dolfuss would be a wild card.
but lets play. lets say that most things remain the same minus Hitler.
Stalin storms across the border into Poland attacks Prussia and the Baltics.sweeps south into Romania,
so the westward drive is rather tough since the poles are fighting hard against the onslaught with the germans and Czechs/Slovaks standing united, helping them to push back the red tide. Austria pushes north and gets told to go home or else, Austria pushes into hungary .. and gets bitch slapped. Austria looks at france and bows out.
Italy.. hrmm.. they attack Albania, send reinforcements to help stabilize Austria which by this time has overthrown dolfuss only to be meet at the new southern German border of the state of Austria.
Finalnd joins the Central Allied powers to fight the soviets as do all the remains of the overrun Baltics, followed by Denmark joining the fight. Sweden is natural at this point but is not a soviet friend.
America, The UK and France make lots of money selling weapons to the central powers.
Italy meantime is bogged down trying to invade Ethiopia. yet no one cares as they are not deemed an honest threat, so the primary focus is on stalling the soviet lines and liberating Poland, Baltics and finland.
Yugoslavia joins the soviet side and presses against Bulgaria and greek claims. the british then become involved in the Balkans.
the Russian lines are stable around the polish german border but no advance over the next year.
Italy does the unthinkable and attacks france thus bringing france into the war full time.
Japan goes for revenge and bombs Vladivostok and invades tying up Russian forces in the far east. this has the added effect of drawing away criticism of its war of aggression with china.
France pounds on Italy, Mussolini is removed from power and Italy withdraws from the war.
Yugoslavia is defeated.
German missile technology and jets come into full production ( this technology shared with british and French forces as well ) this gives them a stark advantage over the soviets.
The Soviets are defeated after the germans explode several atomic bombs on the soviet union . a new Russian democracy is born. Poland, the Baltics, Ukraine, Lithuania ( including Belarus ) are independent nations.
the Russian far east is broken up, the USA purchases land from the Russians. Japan annexes Vladivostok and are towards korea.