In a large saucepan, bring water to a boil. Add pearl onions; boil for 3 minutes. Drain and rinse in cold water; peel and set aside.
In another large saucepan, bring the vinegar, syrup and brown sugar to a boil. Reduce heat; simmer, uncovered, 15 minutes or until liquid is nearly reduced by half. Add cherries; simmer 3-5 minutes. Remove from heat; set aside.
Preheat oven to 375°. Cut a pocket in each duck breast. Stuff with sage; sprinkle with 1-1/2 teaspoons salt and 1/2 teaspoon pepper. Place skin side down in a large skillet. Cook over medium-low heat 10-12 minutes or until most of the duck fat has melted. Turn; cook 2-3 minutes or until lightly browned. Reserve drippings.
Transfer duck to a 15x10x1-in. baking pan. Bake, uncovered, 15-22 minutes or until meat reaches desired doneness (for medium, a thermometer should read 165°; well-done, 180°).
In duck drippings, saute sweet potatoes and pearl onions 6-8 minutes or until lightly browned. Stir in broth, wine, cumin, and remaining salt and pepper. Cook 3-5 minute or until potatoes are tender. Stir in pecans if desired. Serve with duck and cherry sauce. Garnish with parsley.