I know relatively little about Finland, and much of what I know I learned from the fictional 1632 universe by Eric Flint - his Swedish army has Finnish cavalry. Here's another book that I might have enjoyed as a child. It's a mix of Finnish myth and Finnish history.
The protagonist Vaino was named for a Finnish god and the myths (told/sung by the boy's mother were from the Kalvala I presume) were interwoven between various events. Finland's history is one of repeated invasions and most get a men