I just noticed that https://community.openstreetmap.org/t/is-a-channelized-river-still-a-river/127905/ refers to https://wiki.openstreetmap.org/wiki/Tag:channelised%3Dyes ("channelised=yes") which is not widely used but at least documented, so probably superior to my previous guess "river=canalized". Do you know Korsnäs kanal good enough to decide whether such a tag might be sensible?