Well. About adding Finnish strugle to the game aint too important. Btw. I am a Finn.. As there is only the Karelian isthmus on the map and Finland had only one "army" positioned there. The Karelian Army, it was small one if compared to German or Russian Army. And also this game is grand strategy in scale where small Finnish units are difficult to implement. Finns would need uberstatus to do any good on battle. As historic point of view usually one depleted finnish infantry battallion fought against much bigger Soviet formations, sometimes one battallion against division. 1941-1943 Finnish Army outnumbered Soviets though as Finnish Front was secondary and static one.
About those movies.. I prefer the old (1955) Tuntematon Sotilas (Unkown Soldier, http://us.imdb.com/Title?0048752 )
Its the best war film that describes pretty well the war in finnish point of view. Its not about the Winter War though, but about the Continunation War 1941-1944.
Talvisota (Winter War, http://us.imdb.com/Title?0098437 ) Is pretty good also.
Then there is newer version of Tuntematon Sotilas (1985) http://us.imdb.com/Title?0090215