Duck is what makes this one darker and deeper than the pork it is otherwise shaped like. Rillettes de canard are duck meat, often the leg, cooked slowly in rendered duck fat until it shreds and binds into a paste that reads browner, gamier, and longer on the palate than the pork default. The strands are a touch firmer and the flavor has a savory, almost iron depth that pork rillettes do not carry; the duck fat itself tastes richer and sets a little softer. The build is a crusted baguette, split, a thick layer of duck rillettes pressed into the crumb, and little else, so the bird is what you taste.
The logic follows from that depth. Duck rillettes are intense in a way that runs longer and darker than pork, so the sandwich still needs no butter or cheese to feel substantial, but the counterweight has to work harder against a gamier richness: a sharper mustard, a few cornichons, sometimes a spoonful of fig or onion confit whose sweetness suits duck the way it does a confit leg. The paste is still the filling and the binder at once, settling into the open crumb and holding the loaf as one mass, so the bread has to have a real crust to stay structural under a heavy, yielding spread. It eats cool and best at room temperature, where the duck fat is soft and carries the flavor; chilled hard, it tightens, mutes, and turns waxy faster than a leaner spread would.
Variations stay on the southwestern duck shelf. A version cut with shredded confit leg reads meatier and coarser; a smoother pack spreads finer and tastes more uniform; a thin layer of foie gras worked underneath pushes the same animal richer still. Each holds the potted, shredded duck as the fixed point and adjusts only its grain or what sharpens it. The Sandwich Rillettes de Canard belongs with the cured-meat sandwiches the catalog groups under Sandwich Saucisson & Charcuterie, the tradition that runs across France's regional curing shelves. Its specific contribution is a darker, gamier rillettes whose depth comes from duck and duck fat rather than pork, asking for a sharper note to keep it honest.