[quote]Otherwise don't sweat too much over it.  Odds are that nothing bad is going to happen.
Painters on all boats.  PFDS on at all times.  Most boating accidents are the result of poor judgment & plain honest stupidity. [/quote

One way to look at it. I'm assuming your " group leader"?
My question to you is, " IF something bad happens, what would you be willing to do to save a life? Risk others lives no matter the odds? Do what's prudent and live with the consequences? When something bad happens there's little comfort in knowing it was a long shot.

Practicing the self rescue techniques Preacher mentioned in a inland lake may or may not help your cause. Even if they can do everything mentioned, in the frigid waters of Superior with your body going numb in minutes, I doubt any but the most experienced canoeist's could pull it off. It might give them a false sense of safety/competence that won't translate in the frigid Superior waters.
PFD's are great, they'll keep above water and save energy you'd use treading water without them. Painters are great too, but unless you could secure a line to the PFD of the dumped canoes occupant they probably wouldn't be able to hang onto a line for very long if at all.
I have a D-Ring on the chest of my PFD. I suppose if you rigged a Carabiner with a spring loaded gate to each canoes stern painter and could somehow clip to PFD of person in the water, you could then kneel and tow them into shore?
I mentioned before that on one backpack trip on Isle Royale, we were camped at Windingo waiting to take the shuttle back around next day to Rock Harbor and our flight home. We ran into a solo kayak-er that had dumped coming into Windingo Harbor running from a sudden squall on the open water.
He had a full wet suit and it was all he could do to get his kayak righted/bailed even in the calm waters. In the open waters, he didn't think he wouldn't been able to do it. Said he probably would of bailed and swam for shore.
I still think the tandem/ 2 solo's is the best compromise between prudence/safety and the odds that nothing is probably going to go wrong.
IF you can convince them to go that route, maybe you can try a real world experiment. If I remember correctly, there are some very nice campsites right out on Superior. One I remember had a nice little protected bay, sand beach, relatively shallow shelf.
Put on your bathing suits/PFD's go out waist/chest deep and dump your empty solo canoes and see who can get back in on their own. Who can feel their extremities after a few minutes :o
Then you can talk about a 4 solo trip ;)