Heat oven to 250°F. Spray 2 (15x10-inch) pans with sides with cooking spray. In 6-quart bowl, mix oats, both cereals, the walnuts, almonds and sunflower nuts.
In 2-quart saucepan, cook brown sugar, oil, honey and water over medium-high heat 3 to 5 minutes, stirring constantly, until brown sugar is melted. Remove from heat. Stir in vanilla and almond extract. Pour over cereal mixture; stir until well coated. Spread mixture evenly in pans.
Bake 1 hour, rearranging pans once halfway through baking. Cool completely in pan, about 1 hour. Break into pieces. Store in tightly covered container. Serve as breakfast cereal, snack or as topping for ice cream, yogurt or fresh fruit.