Preheat oven to 400°.
Peel onions. Cut 1/2 inch off top of onions; discard tops. Place onions, cut sides down, in an 11 x 7-inch baking dish coated with cooking spray. Pour 1/2 cup wine over onions. Cover and bake at 400° for 30 minutes. Uncover; turn onions, and bake 20 minutes. Turn the onions again, and bake an additional 30 minutes or until tender. Cool onions slightly. Carefully remove pulp from onions, leaving a 1/2-inch-thick shell. Chop pulp to measure 3/4 cup. Combine pulp, breadcrumbs, and next 4 ingredients (breadcrumbs through pepper) in a medium bowl. Add 1/2 teaspoon salt, tossing to combine. Sprinkle 1/8 teaspoon salt over onion shells; stuff shells with breadcrumb mixture. Bake at 400° for 15 minutes or until tops are golden.
Combine remaining 1 1/2 cups wine, 1/8 teaspoon salt, sugar, and rosemary in a small saucepan; bring to a boil. Cook 15 minutes or until reduced to 1/2 cup. Serve sauce over onions.