This cocktail is a variation on the Jean Lafitte drink created by Adam Larkin. It is basically the same drink, only substituting a citrusy soda like Sprite or 7UP instead of sparkling wine.
Sprite/7UP/Squirt (roughly 9 oz)
3 oz Expedition Rum
1/2 oz Grenadine
Orange Juice (roughly 1-2 oz)
Fill up a champagne flute halfway with Sprite/etc, then add in Expedition Rum, grenadine and top with Orange Juice. Enjoy!