I know a few places along Sörmlandsleden, which has a trail head in Mariefred, and even a good kanot route in the area. I am off of work from 20th of June until 20th of August, so all those dates work for me
I'm up for either kanot or hike, have access to a pair of Canadian kanots. We are two adults and two kids, 8 and 10 years old.
Mariefred is full of nice cultural things to see, such as an old castle from the late 1400s, "Gripsholms Slott" and a church from 1628. Marvikarna in Åkers Styckebruk is a beautiful kanot route, and it is relatively easy to transport the kanots by car to the beginning of the route from Mariefred. I know that KanotKungen is willing to help with such things, if we rent kanots from them.