The first time I rented a car for a trip to Canada I asked the desk agent if crossing the border was permitted, just to be sure (like you). The rental was just for a weekend, so found it humorous when the agent replied that Canada was fine, I just couldn't drive the car into Mexico.

Check this site for a list of wineries: http://www.canadasouthwinetours.com/wineregion.html

and take lots of bug spray. The mosquitoes at Pt Pelee are plentiful and hungry.