RV Site UP Michigan - Finger Lakes

Sampson is a nice park. In the immediate area are a plethora of Wineries, and distilleries. The former Seneca Army Depot has White Deer tours,The LDS church has the Peter Whitmore Farm in Waterloo if you are interested in the history. Geneva has become somewhat of a foody destination.
Taughannock Park is also a nice park although older and tighter than Sampson. Has the highest single drop falls East of the Rockies. Ithaca with Cornell is 8 miles South.

Lots of choices.

There's a state park that is highly rated just over the bridge

Picture rocks
Taquamana falls
Procupine
Copper harbor

Take M26

Can take a boat over to Isle Royale

Go over to Mackinac Island

Mackinaw City just on the south side of the bridge

If you are camping near Lake Superior take an extra sweatshirt or two. The wind can be quite cool off of the lake.

Are you going to Michigan or New york?

Another NY SP is Sampson State Park

If you're going thru Wisc to the UP do your self a favor and stop at Little Girls Point County Park. Want to see the great lake? You'll be camped on its shore. Electric only. No water to speak of, nor dump. Gravel sites, no showers, pit toilets. But lovely.

While a bit west of the finger lakes, Letchworth State Park is worth a visit. 150 miles southeast of Letchworth is Ricketts Glen State Park in PA. 21 waterfalls along a 7 mile hike.

I would wait to go to the UP mid to late July. Still can be cold and rainy earlier than that.
I would stay around Munising. We stayed at Munising Tourist Park Campground right in the lake. They do have lake front sites.