My wife and I stayed at Nelson's Resort on Crane Lake, MN near the Minnesota/Canada boarder a couple summers ago and had a good time. They had a nice sandy beach in a protected bay next to the cabin we stayed in and a bar and restaurant that was pretty hopping by local standards. It's also conveniently adjacent to Scott's Seaplane base (KCDD) which is definitely worth a visit if you're in the area.
https://www.nelsonsresort.comI've not been myself, but other local seaplane folks have recommended Hungry Jack Lodge near Grand Marais, MN (0G5 & KCKC). The airport has fuel available both on the hard surface and dockside on Devil's Track Lake (call ahead fuel truck). Fun little town if you can get transportation there. Biking is possible but there's a largish climb between town and the airport.
https://hungryjacklodge.com/If you venture more inland towards central MN, there is Madden's Resort on Gull Lake, outside Brained, MN. M16 is the seaplane base on Gull Lake and 9Y2 is the grass strip a couple miles away. The owner/manager is a seaplane guy so beaching at the resort should be possible (we do it every spring during the MSPA seminar weekend) or they will send a van to pick you up at the grass runway. Good trail and road biking in the area.
https://www.maddens.com/Another fun stop might be Three Lakes (40D), in N central WI, a grass strip right next to the lake. There is a restaurant & ice cream shop right on the water off the runway. There is a beach next to the restaurant which would probably work for your Lake, but I've always found room to tie up at the dock. I've only been there for day trips so don't have any recommendations for lodging, but it's a touristy area, so I'm sure Google would find something for you. The road biking is pretty good in that area too.
Let us know where you end up going. I'm always interested in finding new places that are seaplane friendly.
Mitch