I like the Mannerheim quote and was unaware that his wife was Russian.
Finland took back both the annexed areas lost in the Winter War and then annexed a good amount of Russian
eastern Karelia.
Finnish military administration in Eastern Karelia | Wikiwand
Aunus expedition - Wikipedia (earlier annexation effort)
Private Finnish militias from Finland proper had tried to annex eastern Karelia during the Russian civil war, but were turned back a lack of numbers, communist strength and...... luke warm attitudes from Finnic eastern Karelians.
Though Finns and eastern Karelians are closely related, eastern Karelians are eastern Orthodox and have more eastern cultural outlook. They also had long memories of a war with Protestant Sweden that led to a lot of destruction of Eastern Orthodox shrines, monasteries etc. Western Finns had served in Swedish armies.
Though not hostile to Finnish occupation / annexation
per se in WWII, there was little enthusiasm for it. As a side note, Mannerheim had to relieve a Finnish Lutheran chaplain whose sermons had gotten more than a little critical of Orthodox religious practices and were alienating locals.