Melt butter in 13x9 1/2x 2-inch pan. Sprinkle brown sugar evenly in pan. Drain pineapple; save syrup. Arrange pineapple and cherries, rounded side down, in sugar mixture.
Add enough water to pineapple syrup to make 1 1/3 cups liquid. Add this and 2 eggs to the cake mix. Mix as directed. Pour batter over fruit.
Bake at 350 degrees F. for about 50 minutes, until cake pulls aways from side of pan. Let stand 5 minutes for topping to begin to set. Then turn upside down on a large platter or cookie sheet. Top servings with whipped cream, if desired.