Heat oven to 250°F. Spray 13 x 9-inch baking pan with cooking spray. Place cereal in pan. Place margarine in 2-cup microwaveable bowl. Microwave on HIGH 45 seconds or until melted. Stir in sugar, syrup and vanilla; mix well. Pour over cereal; stir to coat evenly. Bake 1 hour, stirring every 15 minutes. Remove from oven; stir in caramel corn. Transfer to baking sheet, spreading mixture in even layer. Cool completely. Makes about 12 cups (about 24 1/2 cup servings). Store tightly covered at room temperature up to 5 days.