I have never sailed the Göta kanal my self, but I hear it is nice. In which direction did you go? West -> East or the other way?
from east, stockholm, to west - goteborg.
That would be in the far north then and it is true there. In the south we have some really hot summers.
we had great weather - warm, calm... a few days of light rain that didn't last more than a few hours - quite pleasant.
and the whole kanal trip was a wonderful beginning that ended on our side of the atlantic in the virgin islands.