Preheat the oven to 350 degrees F (175 degrees C). Grease a 10-inch fluted tube pan (such as Bundt) with cooking spray with flour.
Pour melted butter into the bottom of the prepared pan. Sprinkle brown sugar evenly on top. Drain pineapple rings over a measuring cup; reserve juice. Cut rings in half. Alternate placing halved pineapple rings and maraschino cherries around the pan. Set aside.
Combine cake mix and pudding mix in a large mixing bowl. Pour enough milk into the reserved pineapple juice to make 1 cup of liquid; add to cake and pudding mixture. Pour in vegetable oil. Mix on low speed, adding 1 egg at a time, until blended. Increase speed to medium; mix until thoroughly combined and smooth, about 2 minutes. Pour batter over pineapples and cherries in the pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 35 to 40 minutes. Let cool for 10 minutes before removing from the pan.