The reason to invade Finland wasn't sue to Nazi collaborationism, Finland still wasn't allied with the Nazis. The reason was the need for the USSR to put additional territory between themselves and the Nazis due to the geography of the region, i.e. the Great European Plain, a vast flatland without natural defenses that is very hard to protect from Nazi blitzkrieg. USSR attempted negotiations with Finland to gain terrains to have control over lands further from Moscow, Leningrad and the oil fields at the south of Russia, and only when those negotiations failed did the Soviets invade. This isn't just explicitly what the Soviets were saying at the time of negotiations, it was openly said so by all western leaders at the time of the Molotov Ribbentrop truce:

“In those days the Soviet Government had grave reason to fear that they would be left one-on-one to face the Nazi fury. Stalin took measures which no free democracy could regard otherwise than with distaste. Yet I never doubted myself that his cardinal aim had been to hold the German armies off from Russia for as long as might be” (Paraphrased from Churchill’s December 1944 remarks in the House of Commons.)

“It would be unwise to assume Stalin approves of Hitler’s aggression. Probably the Soviet Government has merely sought a delaying tactic, not wanting to be the next victim. They will have a rude awakening, but they think, at least for now, they can keep the wolf from the door” Franklin D. Roosevelt (President of the United States, 1933–1945), from Harold L. Ickes’s diary entries, early September 1939. Ickes’s diaries are published as The Secret Diary of Harold Ickes.

"One must suppose that the Soviet Government, seeing no immediate prospect of real support from outside, decided to make its own arrangements for self‑defence, however unpalatable such an agreement might appear. We in this House cannot be astonished that a government acting solely on grounds of power politics should take that course” Neville Chamberlain House of Commons Statement

They weren't doing that when Stalin invaded them. Stalin squandered any advantage he could have possibly gotten by collaborating with the Nazis through invading Finland. Which ironically, pushed the Fins to actually ally with the Nazis.

And why the hell did Stalin invade Poland? The guy sounds less and less competent the more you learn about him, doesn't he?