Catahoula Lake, LA if you are open to that. A crazy percentage of Canvasbacks winter in this location.
Lance Vick (fishing and hunting guide) will typically offer some Canvasback specific hunts once he starts seeing birds too.
You can check with Jeff Elder, he just had a Canvasback shoot.
Don't let your ears hear what your eyes didn't see, and don't let your mouth say what your heart doesn't feel