Nick Carter auditioned for a spot in the same lineup as Britney Spears, Christina Aguilera, Justin Timberlake and Ryan Gosling. He was offered the part but turned it down because he'd been invited to help form a vocal group which eventually became the Backstreet Boys. MMC was canceled a year later.
Jessica Simpson and Matt Damon tried out for, and came very close to getting, spots on the show. They were beaten out by Britney Spears and Christina Aguilera.
The only cast member who didn't return for the final season was Keri Russell. She left the series to film Daddy's Girls (1994), a show that didn't make it through its first season.
During a 2013 interview with the "Stories of the Magic" podcast; Mouseketeer Jennifer McGill mentioned that she, along with Chase Hampton and Tiffini Hale, had auditioned for a proposed movie based on the original Mickey Mouse Club titled "Why, Because We Like You"; only for the movie to be tabled shortly after final auditions due to the 1988 Writer's Guild strike; resulting in their tapes being moved over to the auditions and their subsequent casting.