Ok here's a rough scenario:
Instead of carving up Poland with Stalin, Hitler allies with the Poles and effectively vassalizes them (return of Danzig and the Corridor in return for a Polish lease on the port, etc). There is no Molotov-Ribbentrop Pact, but Stalin does invade Finland and grab the Baltic states, which Hitler and the Poles ignore for now, but the Soviets don't make moves on Romania. The Germans and Soviets strike a trade deal.
War in the west is sparked by Hitler demanding Belgian territory. Goes roughly as IOTL.
With no MR-Pact, Stalin is more wary of Hitler, but he is too cautious to strike first as he would have to go through the Eastern Axis "bulwarks" of Poland, Hungary, and Romania first. German-Soviet trade continues.
Operation Barbarossa (this time with the support of Axis Poland). Even though the Soviets are more well-prepared, it is still a devastating blow. The Axis get further into and smash up more of the USSR. The Holocaust is more horrific in Eastern Europe due to the cooperation of the Polish state, and the Arrow Cross and Iron Guard coming to power earlier in Hungary and Romania, respectively
By the time the Soviets have turned the tide and pushed back the Axis, the Allies have gotten much further into Germany and taken most of Austria, have liberated Czechoslovakia themselves, and have landed in the Balkans to liberate Albania and occupy Bulgaria too. Tito's Partisans liberate Yugoslavia mostly by themselves.
At war's end, the Soviets 'only' occupy Romania, Hungary, Poland, and a small (nonviable) part of Eastern Germany and an even tinier (non-viable) part of Austria.
Stalin withdraws from eastern Germany and Austria, in return for them being demilitarised and neutral. He decides to break up Poland, Hungary, and Romania into smaller constituent regions and directly annex them as SSRs into the Soviet Union, as punishment for their fascist governments and Axis belligerence, full-bore Holocaust participation, and to more fully absorb their resources.
Tito-Stalin split happens. Due to being occupied by the Allies, Albania, Bulgaria, and Czechoslovakia become free-market, democratic, capitalist states that join NATO. Germany and Austria are forced to remain neutral and demilitarised. Finland is still Finlandised.