Although no one seems to know how they got there, the 5th English Iron cannon has been recovered from the Detroit River. Estimated to have been made in the 18th Century, this one will be displayed in a local museum after conservation work is complete.
http://www.clickondetroit.com/news/29394635/detail.html
Three thoughts come to mind, my knowledge of both the area and American history lacking, Battle of Lake Erie if there is under water currents and the battle was close enough to the river, ditched in a retreat that wouldn’t necessarily have to have been British or lost while crossing the river. Would be interesting to know how they really did get there but certainly an interesting find given the other cannons.