I can't speak too much for the Canadian side, but offer the following for the American side:
The State Park as indicated in other posts would be great, but they do not offer full hook-ups.
There are 3 campgrounds on Grand Island: Grand Island KOA, Branches of Niagara Campground and Resort, and Cinderella Campgrounds and Motel. I have only stayed at the KOA on Grand Island, have heard nothing but good things about Branches, and have not stayed at Cinderella. Any of these would offer full hook-ups.
The KOA is right next to a small amusement park called Fantasy Island. It is a nice little park, great for smaller and a little older children. Fantasy Island also has a water park.
Grand Island puts you in easy driving distance to Niagara Falls and Buffalo.
Since you are sticking with the American side here are my personal suggestions being from WNY:
Niagara Falls: I suggest getting the Niagara USA Discovery Pass. This gains you access to the Maid of the Mist, Cave of the Winds, Niagara: Adventures Movie, Niagara Gorge Discovery Museum, and the Aquarium. If you really like adventure and to witness the power of the lower rapids, I highly recommend the Jetboat rides in Lewistown. It is an experience that is amazing.
Buffalo: Buffalo Naval Park is another nice little place, if you enjoy historic war ships. There is also Buffalo Canalside. There are many different activities.
North Tonawanda, NY - Herschell Carrousel Museum is a nice little museum in my home town that showcases one of the main manufacturers of wooden carrousels and amusement rides starting back in 1916. Mid July, depending on your travel dates, would also put you in around the time of Canal Fest which runs along the Erie Canal between Tonawanda/North Tonawanda.
Lockport - you can do a Canal Ride and tour the underground caves
There are various wineries all over the Niagara Region.
Food Suggestions: My favorite place to go for hot dogs is Ted's (they are all over WNY), but if you want to eat by the river, check out Mississippi Mudds or Old Man Rivers in Tonawanda. Western New York is big on Friday Fish Fries. So if you like fish, that is a must. Sadly, I never get in town early enough to enjoy a good fish fry. For Italian food - Chef's restaurant in Buffalo.
Wings - you have Anchor Bar and Duff's. However, I have found that most of the local places make just a good of wings if not better than Anchor or Duff's.
If there is something specific you want to know, just let me know and I will do my best to help you out.
Keep true to the vision living in your head.
Jim & Evelyn
2015 Ford F-350 Dually 6.7L
2016 Prime Time Spartan 1242X
2012 Street Glide (his)
2004 Fatboy (hers)