John,

Not sure what your disagreement with 3 in a canoe is - tandem = more freedom, less restrictions, smaller craft, easier fishing, already have the canoes - but let me offer some thoughts.  I had always thought/prefered tandem and still do for an even number.  Some experience tripling it gave me new perspective. 

A tandem and a solo would slow things down, especially in poor weather or wind.  Your solo would also have a harder time keeping the pace/wear out faster.  Use a Wenonah Minnesota III, not a smaller craft and there is plenty of room for 3 plus gear for 9 days.  I've done it, just leave the kitchen sink at home.  Two Granite Gear #4's and Superior 1 will fit behind the bow paddler and still keep the weight low, then add a small pack (BWJ Guide pack) in front of the stern paddler.  Three motors in one canoe = faster travel on the water = more fishing time/camp time/whatever time.  It is also faster on the portages, loading, unloading, etc.  Less gear overall and more backs carrying less gear = fewer trips across a portage.  A Minn III is only about 5 lbs heavier than a Minn II, but 37lbs lighter than two of them.  Trolling is not that much more challenging with 3....everyone trolls opposite their paddle side.  You would save $$$ renting only one canoe and even more not hiring a 4th paddler, which if you need/want the guide services that is fine.

I would not settle for any smaller boat for 3.  Made the mistake of taking a Bell Northwoods (18.5') into Wabakimi in 2012, as the outfitter did not have the Souris River for 3 they said they would have.  It was not set up properly, making the trip very crowded until we ate our way trough most of the food pack.  The third seat was smack in the middle of the boat and made loading hard.  The Bell is a fantastic canoe and performed superbly, even in some serious waves we shouldn't have been paddling in, but it was just cramped for 3 IMHO.

pd