Heat oven to 350°F. Spray bottom of 15x10x1-inch pan with cooking spray. Drain and reserve juice from pineapple; cover and refrigerate pineapple tidbits.
Transfer reserved juice to 2-cup measuring cup; add enough water to make 1 1/4 cups liquid.
In large bowl, beat cake mix, pineapple liquid, oil and eggs with electric mixer on medium speed 2 minutes, scraping bowl occasionally.
Pour into pan. Bake 20 to 25 minutes or until toothpick inserted in center comes out clean. Cool 5 minutes.
With handle of wooden spoon (1/4- to 1/2-inch in diameter), poke holes almost to bottom of cake every 1/2 inch, wiping spoon handle occasionally to reduce sticking.
In medium bowl, beat pudding mix and milk with whisk 45 to 60 seconds or until slightly thickened but still pourable; stir in rum.
Carefully pour over cake, spreading evenly over surface. Work back and forth to fill holes, tapping pan lightly on counter several times. Refrigerate 2 hours.
In chilled medium bowl, beat whipping cream and sugar with electric mixer on high speed 3 to 5 minutes or until stiff peaks form.
Spread on top of cake; top with coconut and refrigerated pineapple tidbits. To serve, cut into 6 rows by 4 rows. Cover and refrigerate any remaining cake.