Long north-south border on the east parallels the single highway highway and rail line to the Kola Peninsula, home to Russia's northern fleet and multiple military airbases. Heavily forested, sparse population. Perfectly suited to special forces operations against Russian supply lines.
East if Helsinki is a completely different topography. This is where the Winter War of 1939 was largely fought. Forests, lakes and marshes. Finland “lost” the winter war largely because they ran out of bullets. Neither Sweden nor Germany would sell them munitions.
Russian Navy and commercial shipping would largely be bottled up in St. Petersburg. Access between the Baltic and St. Petersburg is through a small gulf that freezes in the winter and lies between Finland and Estonia. The navigation channel is a mile or three wide over much of its length. Lay out a mine field, a pile of antiship missiles and poof St. Petersburg is corked up.
You know your Finland vs Russia stuff! I learned something. Bottom line is that no nation wants to be under the Imperialist Russian boot. They are greedy, incompetent idiots.
As their army has recently shown in Ukraine.