For an easy substitution, Sprite can be used in place of 7UP in Paula Deen's 7UP Cake. They are both colorless, caffeine-free carbonated sodas that feature a lemon-lime flavoring.
Another soda to consider as a substitution is Sierra Mist, as it shares these similar qualities with 7UP and Sprite. The soft drink 7UP was created in 1929, and Sprite was introduced in 1959, so 7UP is considered the original lemon-lime soda. Paula Deen's classic recipe calls for 7UP in both the cake and the frosting, so it is important to choose a soda substitute that is colorless, so the overall tint of the finished product is not affected.