Canoe Size

There isn't much debate on this issue. A tripping canoe should be a minimum of 16 ft. long ... and that's a bare minimum; and if it is to be used for longer trips, it should probably be at least 17 ft. Canoes used on extended trips will often be 18 ft. or longer. Canoes shorter than 16 ft simply do not have the volume required to carry a large load of gear and keep it dry.

Is there a tradeoff involved in length? 

Of course, as with everything related to canoe design. Longer canoes are generally capable of faster speeds, and will handle large rolling swells better. 

Shorter canoes are more maneuverable and will handle whitewater better because of their shorter turning radius.