Carefully cut a pocket into the duck breast lengthwise being careful not to cut all the way through. Combine the vinegar, melted butter, and olive oil, with a little salt and pepper in a bowl, with duck breast, and marinate for at least 8 hours, refrigerated. When ready to grill, remove breast from marinade. Macerate the dried cherries in 1 cup of the Champagne for 10 minutes. Pour the rest of the champagne in a saucepan and simmer, until reduced to 1 cup; set aside and let cool. In a small mixing bowl, mix together the goat cheese, macerated cherries, and walnuts until well combined. Stuff each duck break with the mixture and seal with a toothpick.
When the Champagne has cooled to room temperature, stir in the sugar. Before the sugar begins to dissolve, brush the mixture onto the duck breast and place on a preheated grill. Grill 3 minutes on 1 side; then turn 45 degrees to create nice grill mark crosshatches. Continue to brush the duck breasts with the glaze while cooking. Flip the breast and cook on the other side, until cooked through, slightly pink inside. In the last seconds of grilling, place the breast on the hottest part of the grill for 8 to 12 seconds to sear. Plate and serve immediately.
Serve with roasted root vegetables like cubed butternut squash, acorn squash, and parsnips, or maple syrup whipped sweet potatoes.