Line a 9x9 baking pan with parchment leaving a 3 inch overhang and set aside.
In a large bowl, mix together the Cheerios, banana, cherries, coconut and sunflower seeds. Set aside.
In a large saucepan, melt the butter over medium heat. Stir in the marshmallows and stir constantly until the marshmallows are completely melted. Pour the mixture over the Cheerios mixture and stir to coat. Pour the mixture into the prepared baking pan and press down with your hands to form an even layer (this works well if you coat your hands with butter or cooking spray). Allow the mixture to cool completely and then remove by pulling the bars out of the pan with the parchment and transfer to a cutting board. Cut the cereal into 12 bars and wrap individually before storing at room temperature in an airtight container. Bars can be stored up to 5 days.