Toronto would actually prove to be a fair bit better than 8 hours from Chicago, particularly by the time you factored in the time to get out of the Chicago metro area and to clear customs at the border. I like Mark's idea of once around Lake Michigan. One great stop along such a route, and perhaps a destination for such a trip would be Sleeping Bear Dunes National Lakeshore. Note that while there are a few restrictions they generally welcome pets. Be sure to read their page on pets. And read these hints on travelling with pets.
Another nice natural setting on the northwest shore of the lake is Hiawatha National Forest. And for a little history, take a stroll through Historic Mackinac at the top of the lake.
AZBuck