It's a Rob Roy-style double-paddle canoe, much like the pair of mine you are babysitting...
It's got a forward mast step for a downwind sail rig, but no provision for a centerboard.
B.B. Crowninshield is indeed a well-known yacht designer who is known to have designed some sailing canoes (notably Uncle Sam and Old Glory. W.F. Stevens was one of the finest sailing canoe builders, first in Lowell, MA and later in Bath, ME. Among others, he built Leo Friede's Mermaid, and most of Paul Butler's canoes.
I can't see enough detail to know if Stevens built this canoe or not.