I’ve had it with off-dry Riesling: Alsatian and Kabinett and Spatlese from Germany. The acidity of a good Riesling does well to cut through the richness of the duck and the sweetness marries well with the flavors in my opinion.
Hmmm. The blood sausage is throwing me a bit there, let’s see what the experts say. Taking a wild guess if you want sweet, would port be off base? Otherwise richer Alsace but really I’d be into reds I think. Cru Beaujolais from a river year.
Obviously, reds are what you’d expect. I take it from Jim’s (OP) post that he’s trying to think outside the box, so suggesting reds is really kind of ignoring what he asked for.
If the choice is a sweet white, I’d lean toward something with good acid and/or bitterness from botrytis – something to counter the richness of the food.
We have lots of confit because my wife is from Les Landes where most of it comes from. I must say that the idea of a sweet white rather threw me, especially since the confit is backed up with a boudin!
But many enjoy the latter with apple, so why not?
I suppose it also depends on how you cook the confit - crispy or soft skin - and whether you eat the skin or not.
I would certainly be most at ease with a Madiran or a Cahors, but the safest option would be to experiment with two or three different choices: one of the two above, plus a demi-sec Vouvray, as Nate suggests, and something similar from Alsace.
For a sweet white with duck confit, go with something with enough age that the wine has started to darken, like a 1996 or earlier Baumard Quarts de Chaume. There will be additional richness to harmonize with the deep savory qualities of the confit.