Prep: 12 minutes. Make the juice the night before, cover, and store in the fridge. Be sure to give it a stir before adding the sparkling wine.
Remove the skin from the pineapple. Cut it lengthwise into quarters. Cut off the thick core from each quarter. Slice 2 of the pineapple quarters lengthwise into long spears; wrap in plastic wrap and refrigerate until ready to serve.
Chop the remaining pineapple quarters into chunks. In a food processor, puree the pineapple with 1/2 cup of the orange juice. Pour into a large pitcher.
Using the processor, puree the bananas with 1/2 cup of the orange juice. Stir into the pitcher. Add the remaining orange juice, maple syrup, grenadine, and lemon juice. Cover and refrigerate until well chilled.
In each of 12 tall glasses, pour 1/2 cup juice and 1/2 cup sparkling wine. Garnish each with a pineapple spear.