Place 2-gallon resealable food-storage plastic bag in stockpot or very large bowl.
Add cold water, 2 cups vinegar, the sage, peppercorns and garlic to the bag.
In medium bowl, stir together 1 cup boiling water, the salt and brown sugar until dissolved.
Pour into vinegar mixture.
Remove excess fat from body cavity and neck of duck.
Rinse inside and out under cool running water.
With large sharp fork, prick the skin all over at an angle, being careful not to pierce meat.
Carefully place duck in brine, making sure entire duck is submerged (weigh it down with a plate, if necessary).
Cover; refrigerate at least 12 hours but no longer than 24 hours.
Heat oven to 350°F.
Remove duck from brine; discard brine.
Rinse duck inside and out and pat dry.
Place duck, breast side up, on rack in large roasting pan.
Tie legs with kitchen string.
Insert ovenproof meat thermometer so tip is in thickest part of inside thigh and does not touch bone.
Roast 1 hour 40 minutes.
Carefully remove duck from pan; pour drippings and cooking juices from pan into large heatproof bowl or container.
Discard or save for another use.
Return duck to rack in roasting pan.
In medium bowl, stir together cranberry sauce, ¼ cup vinegar and the chiles; reserve half of the glaze for serving.
Brush about ¼ cup of the remaining glaze over duck.
Roast 45 minutes to 1 hour longer, brushing with glaze every 10 minutes, until meat thermometer reads 165°F.
Place duck on warm serving platter.
Cover; let stand 15 minutes for easiest carving.
Heat reserved glaze until warm; serve with duck.