I have very few datapoints, mostly from Finnish court cases from early 1700s after Great Nordic War.

Orthodox Christians were manumitted: there was a Finnish woman taken into slavery but converted and was probably baptized in order to get manumitted. She worked as domestic servant before and after her manumission. She got charged (for her baptism) when she returned from Russia after the war ended.

People that did not convert or were not given chance to convert were treated as chattel: a few were traded to Turkish and Persian, there were accounts of people sold to Persian slave markets and bought back by Swedish travelers. One returned only to find his wife had married to another man.