Combine sugar, water, butter, and cinnamon in a 5- to 6-quart Dutch oven. Bring to boiling over medium heat, stirring constantly. Continue to cook for 4 minutes more, stirring occasionally. Remove syrup from heat.
Add the popcorn, cereal, cashews, and raisins to the syrup; stir quickly to coat all ingredients evenly. Spread coated popcorn mixture in a single layer on 1 or 2 large baking sheets lined with waxed paper or parchment paper. Cool completely. Break up any large pieces. Store in an airtight container at room temperature for up to 3 days. Makes 12 cups.