I was waiting for someone else to mention the ultimate American Road Trip, Route 66.
In terms of 'Driving Roads', Route 66 doesn't cut it since it is now mostly Interstate 40 & 44, but there are still some off-interstate roads through small towns that are considered Route 66. Route 66 may no longer be about The Road, but it sure qualifies as the great Road Trip experience. There are still several of the historic attractions to see (eg. the Blue Whale, Cadillac Ranch, the Bluebird Motel, etc.) and lots of books available to guide you to the rest.
When my family drove the route in 1995, I set out to collect all of the Route 66 road signs for each of the 8 states along the old route. There are lots of different styles of the signs, and you can buy them as a set, but I wanted to collect one particular style and I wanted to buy it in it's 'home' state. That turned out to be the secret sauce that made our Route 66 adventure our best Road Trip ever.
In order to find the style of sign I was after we had to stop at many Route 66 antique shops in each state. Every shop was the kind of adventure that we could have only hoped for. There were so many elderly and interesting people in all those shops that had lots of stories to tell and items to show us. Every shop was an adventure, in addition to the adventure of finding them. I remember our Route 66 trip as mostly a series of attractions, shops, and people, much like the adventures of Buz and Tod who spent a relatively small amount of their time actually on The Road.
Besides the many 'official' attractions along the route, there are many other wonderful attractions not too far from the route that should not be missed. Many of them (Grand Canyon, Four Corners, Mesa Verde,, etc.) are reasons for a road trip all on their own.
A couple years after our trip I put together a picture mural of our road signs and my favourite pictures from the various adventures and attractions. This mural is still on the wall in our family room and calling me back to the Road every time I stand and look at it.
After posting my Route 66 report from our 1995 road trip, I became curious about what the Route looks like today, and whether it still makes for a great road trip. I found my answer in this YouTube video, https://www.youtube.com/watch?v=H0bA72fjHMQ that goes well beyond my small report.
Yes Route 66 still makes for a wonderful family road trip adventure.
Eventually the borders will fully open and from Michigan you have Canada. Whether you cross in Detroit or Port Huron you are in for a few hours of driving that is very similar to rural to small-urban Michigan. How much time you want to spend can guide your route selection from there.
Routes along Lake Ontario can be scenic (old Lakeshore Highway). At one point you will even get to do a ferry that is more like a barge that can handle a few cars. Keep on this route you eventually get near the St. Lawrence Seaway where you can see the flooded (for the seaway) town locations, Upper Canada pioneer village and neat towns like Belleville and Kingston which the old parts are all limestone construction. Very different feel and look than most of Ontario. Probably most fun if you have a couple of days and do a stopover in Kingston.
Or... you hit Toronto via the 400 series highways (similar to interstate). 2 hours north of Toronto you will hit Muskoka, where the geography turns to Canadian Shield and mostly evergreen. Off the main highway, Muskoka is full of twisty roads with scenery. Hit up the crazy road to Torrance Barrens Dark Sky Preserve (look that up if into oddball parks).
If you have time, driving the loop to Manitoulin Island and taking the ferry to Tobermory can be fun.
If you have days and days... take highway 17 up along the coast of Lake Superior. Stop at the Terry Fox Lookout.
If you really have time, keep going and experience the big sky in the prairies. Everyone should drive through the badlands of Alberta at least once...