From the south take I94 east
From the west take I69 east
From Ontario take highway 402 west crossing the St. Clair River into the United States via the Blue Water Bridge
The annual [http://en.wikipedia.org/wiki/Port_Huron_to_Mackinac_Boat_Race Port Huron to Mackinac sailboat race] one of the longest fresh-water races in the world with over two hundred boats entering the race each year.
Sarnia is across the Blue Water Bridge in Ontario, Canada.