There is a plethora of sights to see between Minnesota and Grand Canyon. How much time do you have?
Just a few suggestions.....There's Rocky Mountain NP and the whole southwest quadrant of Colorado, including such places as Durango, Ouray, Black Gunnison NP, Mesa Verde NP, etc. Then there's 5 Nat'l Parks in southern Utah. Also Monument Valley and Page/Lake Powell.
I'd take one route out and a different route back.