Soviet Union invades Germany

[WeisseRose]

This may be a bit far afield, but imagine the following:

Hitler stops immediate plans for expansion after the annexation of the Sudetenland, deciding to avoid any chance of war with Britain/France, and calculating that the aggression of the Soviet Union may give him a chance to take territory in the East without starting a war himself. Germany spends the next several years modernizing their industry and further developing their economy. The Soviet Union finishes their military reforms, and sometime around 1943-44, invades Finland, the Baltic states, and Poland (of course this assumes they intended to expand, which I believe they do). Germany immediately declares war on the Soviet Union, in "defense" of Poland. Two parts to the question:

A) What do the Western powers do?
B) How does the war turn out?

Edit: Apologize for the potentially misleading title. Gist is the same but could have clarified as Poland instead of Germany

 

[notgivenaway]

It depends imho on how much Britain and France can deal with Hitler, or potentially ally with him. They knew the USSR was a potential enemy, but then Hitler was the biggest threat, Stalin never wanted to invade other countries.