It starts above the lake. It's quite narrow. Infiterra put a canoe cp up it once and it was bumper boats , good times. I haven't scoped out the exit. It is huge by Proud Lake of course, so somewhere there it must get usable.
You can go well past a2 - the Huron empties into Lake Erie. There are rumblings of a mega paddle if we can ever coordinate. There are canoe only campsites along the way if not done straight.
The Huron-Clinton Metroparks parks put out a really nice "Canoeing and Kayaking Map" from Proud Lake to Lake Erie. It shows/gives a lot of details from start to finish. I picked mine up at REI last year for free. Not sure if you can request one online or not. I keep thinking that "one of these days" i'm going to plan a trip :)
Update, just found this online. Obviously would be much better if you could pick an official one up, but this would do in a pinch (especially if you had a color printer that could print out on larger paper).
I somehow thought the river was flowing out of the western end of the lake. Of course I was mistaken. The stream going south enters a maze of lakes surrounded by subdivisions, I guess it would be easier to start around Wixom somewhere.
Jen and I are planning a 100 mile trip starting at Erie. If we play our cards right, my husband might meet us at ILRA and grill us some steaks on our second night.