Stop at the brown question mark ?
If you cross from Detroit into Windsor, you can find one of these:
WINDSOR HURON ($)
1235 Huron Church Rd.
Tel: (519) 973-1310
GPS Coordinates 83°3'42.3997"W , 42°17'33.9679"N
WINDSOR PARK ($)
110 Park St. East
Tel: (519) 973-1338
GPS Coordinates 83°2'10.422"W , 42°19'2.004"N
There you can pick up brochures and a map of Ontario. You can perhaps exchange money, but you may get better rates at a bank.
On the map of Ontario you will find the occasional picnic table. This denotes a rest area, which may be very primitive compared to rest areas you might find on I-35. Do not expect to have a shower or buy a pastry from a vending machine, but you will find tables, litter barrels, and toilets of some kind. There may be a stream for washing up, but I would not consider that safe drinking water. The farther north you go in Ontario, the more likely it is that you can put up a tent there without being rousted by Ontario Provincial Police.
Do get in touch with the Ontario Stromtroopers.
They are cordial and ready to guide you and swap lies.
The New Englanders are very welcoming as well.
Best of luck on your voyage.