Heat oil in a medium saucepan over medium-low heat. Add fennel and shallots; cover and cook 3 minutes or until tender. Add 2/3 cup grapes and next 5 ingredients (2/3 cup grapes through rosemary). Bring to a boil; reduce heat, and simmer until liquid is reduced to 3/4 cup (about 10 minutes). Strain wine mixture through a fine sieve; discard solids. Return wine mixture to pan.
Heat a large skillet coated with cooking spray over medium heat. Add duck; cook 8 minutes on each side or until done. Let stand 5 minutes; cut into 1/4-inch-thick slices.
Combine water and cornstarch. Add cornstarch mixture and demi-glace to wine mixture, stirring constantly with a whisk. Bring to a boil; cook 1 minute. Add 1/2 cup grapes; cook 30 seconds. Remove from heat; stir in balsamic vinegar, butter, and pepper.