Formal:
* Les futurs leaders: This is the most straightforward and literal translation.
* Les dirigeants de demain: This emphasizes the future aspect and can be translated as "the leaders of tomorrow".
Informal:
* Les leaders de l'avenir: This is a more poetic and slightly more informal way to say "future leaders".
* Les jeunes pousses: This literally translates to "young shoots" and is a metaphorical way to refer to promising future leaders.
The best option will depend on the context of your sentence.