Spray bottom and sides of 13x9-inch pan with cooking spray. In 2-quart saucepan, heat sugar and corn syrup to boiling over medium-high heat, stirring constantly. Remove from heat. Stir in peanut butter until melted.
In extra-large bowl, stir cereal and peanut butter mixture with wooden spoon until cereal is evenly coated. Stir in 1 cup of the candies.
Press cereal mixture in pan. Immediately sprinkle with remaining 1/2 cup candies; press in lightly with fingers. Let stand about 30 minutes until cool. For bars, cut into 6 rows by 6 rows.