Could Finland control the Baltic Sea in a war with Russia?
Short answerProbably not; both sides could contest and use the Baltic, but control would remain local rather than theater-wide.
NotesThe Baltic would be a contested operating space rather than a theater either side could dominate outright. Russia and Finland would both try to use the sea while denying the other freedom of action. Geography, coastal defenses, mines, and nearby bases would favor pockets of local control. The likely result is sustained dispute, with neither navy able to translate local advantage into general command of the Baltic.