Several optionsI can think of:
I-80 to I-39 as has been mentioned.
The SS Badger, as also has been mentioned. It's not inexpensive, though you do save a bit on tolls. I might cut across Canada from Buffalo to Port Huron.
Take e.g. I-75 north to the upper peninsula of Michigan and then US2/US8 across. Again, I would consider going across southern Ontario.
Head up towards Montreal and go across fully in Canada to either Salut Ste. Marie or Thunder Bay. Likely slower, but it's a pleasant and scenic and generally smooth going drive.