The area around Viborg was lost to the russians in 1721 and 1743. The western part of that, Lappeenranta and part of Kymenlaakso, are part of Finland today. https://en.wikipedia.org/wiki/Old_Finland
Gadolin was Finnish by the same logic Benjamin Franklin was American. Or would you consider him an Englishman? He was born in the British colony, after all.
That Finland has a sizable Swedish-speaking minority? The guy was considered Swedish back then; Finland was simply the Eastern half of the Swedish kingdom.
There's plenty of Finnish speaking Swedes too. Is that also an argument for invasion?