I'd love to suggest a great route through southern-border Michigan... but there really aren't any.

That part of the state is indistinguishable from Indiana and Ohio

and the main selling point of the east/west roads in that area is just that they aren't I-80/90.
On the other hand, the
scenic route from the Big Apple to Chicagoland includes a whole lotta Michigan, going by way of Niagara though Ontario to Sarnia/Port Huron, up the Huron coast to Mackinac, then through the UP and Wisconsin... which can also be done in reverse.
There are literally only two roads that go across the UP west/east; coming from the south you'd naturally want US-2, which includes some great views of Lake Michigan at the east end. Be forewarned however: it's a fairly popular east-west route for truckers doing the Ontario/Seattle run (not so great on a 50cc, I can tell you). M-28 (the north route) is notorious for the Seney Stretch, a little bit of Kansas (no turns, no stops, no nothin) through the northern wetlands. On the other hand, it gives you access to Lake Superior (especially Pictured Rocks). I'm told that the route through Ontario after crossing into Canada at Sault Ste Marie is nice... but I can personally vouch for US-23 and M-25 on the east coast of Michigan: not as many beaches as the west coast, but still a nice ride. By the way, the Mackinac Bridge... can be a little unnerving. But totally do-able.
