Armin Zola
One of the prime candidates for Power Broker is someone that was last seen in Captain America: The Winter Soldier, an MCU film from which The Falcon and the Winter Soldier takes an immense amount of inspiration. While Armin Zola was shown to be destroyed in an explosion, it’s not like he couldn’t have been backed up on a hard drive or somehow restored using some of that next-level technology the universe has a lot of lying around.
Zola was The Red Skull’s right-hand man and would definitely have made many contacts in the underworld from his time with Hydra and during the time of The Winter Soldier program to be able to rise to power in such a crime-ridden place. And he would definitely have had a substantial amount of interest in getting his hands on the Super Soldier Serum.
It would also be pretty cool if the show decided to show the character if he is, in fact, back in action as Power Broker with a body like the way he appears in the comics, looking similar to Krang from Teenage Mutant Ninja Turtles.
Justin Hammer
Another candidate for Power Broker has to be Justin Hammer from Iron Man 2, who ran a company that was constantly outdone in the weapons manufacturing game by Stark industries. He ended up going to jail for his actions in the Iron Man sequel, and if he were to have escaped, Madripoor is probably the place he’d go next.
Given his business experience and knack for shady deals, it would not be out of the ordinary for him to find himself dealing in super-soldier serums after his long stint with machines.
It would also make sense as to why he would take on the moniker Power Broker as it would seem that Justin Hammer would be seen as kind of a joke in the eyes of criminals. Also, as someone who has been beaten by superheroes (plus the fact that individuals like Captain America have proven to make his tech look obsolete) it makes sense that he would want to up his game into the superpowers trade, making him a solid choice to surprise viewers in The Falcon and the Winter Soldier and remerge once again.