Planning a trip out of Pickerel in July with my Wife, 9 yr old daughter and 5 yr old son.  Maybe the B-Chain circle.  I have a MNII and have done trips with my Wife and daughter in it with enough room for everyone.  Now it is time for my son’s first trip and I'm concerned about having enough room to safely and comfortably canoe.  We bring three  40 to 50 pound packs, day pack, and the four of us total about 500lbs.
I know of the MN III, IV and Champlain, and Souris River 18.5' as big load canoes.  The MN IV may be the obvious choice but I would like to get some input.