Assistant Coach Willie McGee
This choice is highly unlikely but it would be cool to see. McGee had a long playing career lasting 18 years, 12 and a half of those with the Cardinals. In his Cardinal tenure, he was a 4-time All-Star, a 3-time Gold Glove winner, a 2-time batting champ, a silver slugger, MVP in 1985, and a World Series Champion in 1982. All of these accolades led to McGee getting inducted into the Cardinals Hall of Fame. He has been in the Cardinals organization post-playing career since 2013, starting in the front office but he has been on the coaching staff since 2018 (excluding 2020 where he opted out) helping with outfield defense and base-running.
What makes McGee a long shot is that he does not have any managing experience, and he has only been in a full-time coaching role for 5 seasons now. One positive he has is his relationship with players, he is always approachable, a great instructor, and a great players coach. The question is whether he could do the strategic side that comes with managing in the MLB. McGee will always be a fan favorite, still to this day he gets one of the loudest ovations from the fans out of anyone, but having him be manager would mostly be up to if he wants that added responsibility.
Honorable mentions: Pop Warner, Turner Ward
Again we're just speculating, but if the Cardinals wanted to look outside of the organization there are options there as well.