Cross Country trip from Michigan to Las Vegas
 

My husband and I are planning a trip from Canada via Michigan to Las Vegas in mid September. We are seniors and plan to road trip. We will stay in Vegas for 5 months before driving home. We are looking for places to see along the way as we plan to stop every other day to sight see.

The route that I would follow would include Glenwood Springs Colorado, Moab Utah (Arches & Canyonlands), Monument Valley, North Rim Grand Canyon, Bryce & Zion National Parks on the way to Las Vegas.
If you come back in late February, you may want to take a more southerly route through Texas.

Are you entering at Sault Ste. Marie or Windsor?

If the former, I would drive through the UP and make a stop at Bayfield, WI. Take the ferry out to Madeline Island. Continue west to Duluth and if you have the inclination, head northeast for a few hours along the North Shore of Lake Superior.

If Windsor, you could still head north to the UP, or head east to Chicago.

In either case, I would then head to South Dakota and stop at the Black Hills on your way. After that, head to Yellowstone and Grand Tetons. These are multi-day stops if you really want to see what there is to offer though, so you may want to plan on more than just an overnight.

From Yellowstone you could either head to Las Vegas via Salt Lake City, or backtrack a bit and go through Denver. If you go through Denver make sure you stop at Rocky Mountain National Park on the way.

I'm not sure if you should stop at Bryce and Zion or not. On one hand they are close enough to Vegas that they are easily doable on a weekend. On the other hand, winter will be setting in and Bryce will get a fair amount of snow (even Zion will get some). That would limit your options a bit - you can still visit in winter but it'll be colder and trails can be icy.

On the way home in February, yes, go to the southern route. Big Bend National Park in Texas is out of the way but well worth a few days.