Thank you. I'm intrigued with the possible effects in Poland: Do you think the Soviets have a real chance of victory there in this scenario?
It is hard to say, as there are many moving parts in the successful Red revolutions in Finland and the Baltics. On balance, I would say the Soviet chances in Poland would be better at least. They wouldn't have to worry about their Western flank in the same way they did IOTL, though we have to remember that by the time of the OTL Soviet-Polish war, the Bolshevik government was at least negotiating about peace with the Finnish and Baltic governments and was not directly threatened by their forces. ITTL, though, the Soviets could probably rustle up some additional troops for different duties from these newly Soviet areas, if not to directly take part in the campaign in Poland, then at least to try and keep order in other parts of the Soviet domains.
As I understand it, one of the problems affecting the Polish campaign was that the Bolsheviks were not exactly secure yet in their home front, as it were, and faced internal rebellions (in big part caused by the food shortages). The inclusion of Finland and the Baltics would shore up the Soviet power base in their campaign against Poland, and given how close to victory the Soviets came IOTL, I don't see it as entirely impossible that they would prevail against Poland ITTL.
And who would be good communist/anticommunist/fascist agitators in interwar Sweden? I'm no familiar with that at all.
This would be more of a question for our Swedish friends as Swedish internal politics is not my strong suit, but with my limited knowledge, for the far left in this timeframe (late 1910s - 1920s) I could suggest some members of the Left Social Democrats like Zeth Höglund, Ture Nerman, Karl Kilbom, Otto Grimlund or Sven Linderot. These people were Lenin's collaborators IOTL, and while the Swedish far left recoiled away from Stalinism for the most part, in a TL where the young Soviet state is considerably stronger they would in turn probably support its goals more strongly, especially if it avoids some of the excesses of OTL Stalinism.
With similar limited knowledge, for the far right, we might look at the Swedish Nazis and militarists. In the first group, names like Barthold Lundén of the Swedish Anti-Semitic Union, or leaders and strongmen of the different fascist or right-wing groups like the Furugård brothers, Konrad Hallgren, Sven Olov Lindholm, Per Engdahl or Elmo Lindholm. We might also expect some OTL "borderline cases" to slip into radicalism ITTL, so there might be unexpected figures, people considered merely conservative, rising to prominence. In the militarist group, Colonel Martin Lindström or Count Eric von Rosen might gain more than OTL prominence. ITTL Lindström would very likely fight in Finland or the Baltics for the White cause, like he did IOTL, and if he avoids dying there, I could well see him organizing a domestic group to battle Communism in Sweden, probably along with White emigrés from Finland and and the Baltic states. The support of right-wing members of the Swedish military would be expected - some possible names could be drawn among those men who took part in the Finnish Civil War as volunteers on the White side, say. People ready to risk life and limb to avoid Red rule in Finland would probably feel even more strongly for their own country's future.
In that vein, one pretty unlikely but certainly historically ironic leader for the Swedish anti-Soviet far right ITTL might be Olof Palme, the eponymous uncle to the famous OTL Social Democrat politician who in 1917-18 was a prime campaigner for forming a Swedish volunteer brigade to fight for the Finnish Whites. If he avoids dying in Finland, he might well have a future as an anti-Communist politician.
