Michigan is wonderful in the summer, (right now it's 3 not including wind chill and I'm ready to lose my mind!).
We're all about the water here. I have to politely disagree with the previous poster, I would never encourage anyone to visit the Metro Detroit area. Not exactly a city worth visiting. But the lakes here are fantastic.
I prefer Lake Michigan, it can't be beat. Just throw a dart on a map on the western coast, you can't really mess up. White sand and fresh water as far as you can see. Numerous state parks are on the water and if you can't get a reservation at the campground, you can always stay at a private campground and go to the beach for the day.
If you're looking into crossing the border then you may want to visit Lake Huron instead. You could start north and go to Mackinac Island for a day or two then try to get a spot at Tawas Point State Park before heading over the border. But that's a lot of north to go south driving. You also have the option of Lake Erie, but I have to be honest that Lake Erie isn't worth the drive. Lake Michigan is really where it's at.
Do you realize that Sarnia is only 3.5 hours from Niagara Falls? If you're coming from Texas, I am guessing your kids have never been there. What's 3 more hours to see the falls. The Canadian side is very touristy but the best way to view the falls. TONS to do there.
