The name "canvasback" is derived from the dusty white feathers on its back and sides. English settlers along the Atlantic coast thought these feathers looked like white canvas fabric. Though fewer people hunt "King Can" than once did, everyone should witness once in their lifetime the thrill of a flock of cans ripping over decoys on a crossing wind. http://www.ducks.org/Conservation/Waterfowl-Research-Science/Photo-Essay-Canvasbacks
Some reason this does spark a memory, a story I once heard. Now I think I may need to Google it myself. So, I was told back in the day market hunters would pack canvas bags full of ducks. By train, transporting the ducks to the city. On the bags filled with ducks they would write "canvasback". Meaning please send the bags back. So they could fill them with more ducks. And the ducks they targeted and sold was, now what we know as the Canvasback. And that's how they got the name.?