Heat oven to 375°F. Spray 13x9-inch (3-quart) glass baking dish with cooking spray.
In 5-quart Dutch oven, heat 4 quarts water to boiling. Add macaroni; cook 4 minutes. Stir in carrots; cook 2 minutes longer or until tender. Drain. Return macaroni and carrots to Dutch oven. Stir in broccoli, Alfredo sauce and 1/2 cup of the cheese. Spoon into baking dish.
In small bowl, mix bread crumbs, remaining 1/4 cup cheese and the butter; sprinkle evenly over casserole.
Bake uncovered 25 to 30 minutes or until thoroughly heated and topping is golden.