Spray the bundt pan with Pam no-stick baking spray with flour. Make sure to get every nook and cranny.
Melt butter and pour evenly into the bottom of the pan. Sprinkle with brown sugar. Cut pineapple rings in half and alternate with cherries around pan and set aside.
In a large mixing bowl stir cake mix and pudding mix together. Drain the pineapple juice into measuring cup and add enough milk to make 1 cup of liquid and add to cake/pudding mixture. Add oil. Then add eggs one at a time to cake/pudding mixture until thoroughly mixed with a mixer on medium speed for approx 2 minutes.
Carefully pour the batter over the fruit and bake for 33 to 36 minutes. To avoid spills, make sure to put the bundt pan on a baking sheet.
Cool 10 minutes in the pan. Slide knife around edges and center. Invert cake onto serving tray. Slice between the pineapples and serve warm or at room temperature.