Preheat oven to 300°.
Combine peanut butter and syrup in a small microwave-safe bowl. Microwave at high 30 seconds or until hot; stir well. Place granola and pretzels in a large bowl; pour peanut butter mixture over granola mixture, stirring to coat. Spread mixture in a single layer on a jelly-roll pan coated with cooking spray. Bake at 300° for 25 minutes, stirring twice. Stir in raisins and cranberries; return pan to oven. Turn oven off; cool mixture in closed oven 30 minutes. Remove from oven; cool completely.