Step 1: Preheat your oven to the temperature specified on the cake mix box (usually 350°F) and grease a 9x13 inch baking pan.
Step 2: Prepare the cake mix according to package directions, substituting the water with the reserved pineapple juice from the crushed pineapple. Stir in half of the drained crushed pineapple into the batter.
Step 3: Pour the batter into the prepared pan and bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.
Step 4: While the cake is still warm, use the handle of a wooden spoon to poke holes all over the cake, spaced about an inch apart.
Step 5: In a medium bowl, whisk together the sweetened condensed milk, cream of coconut, and the remaining crushed pineapple. Pour this mixture slowly over the warm cake, ensuring it seeps into the holes.
Step 6: Let the cake cool completely at room temperature, then cover and refrigerate for at least 4 hours, or preferably overnight, to allow the flavors to meld and the pina colada poke cake to become fully moist.
Step 7: In a large bowl, beat the heavy whipping cream, powdered sugar, and vanilla extract until stiff peaks form. Spread the whipped cream over the chilled cake.
Step 8: Sprinkle the toasted coconut over the top and garnish with maraschino cherries before serving your delicious pina colada poke cake.