Sam Wilson: Captain America
Following the funeral scene, Steve is given the task of returning the Infinity Stones to their rightful places in the timeline. He doesn’t return as expected, though, and it’s revealed that he ultimately decided to go back in time and live out his life the regular way with Peggy Carter. When old man Steve reunites with Sam and Bucky, he hands his shield to the former Falcon and encourages him to be the next Captain America.
This is a very similar scenario to the origins of Sam as Cap in the comics. The only difference is that Steve didn’t go back in time but had the super-soldier serum in his system neutralized so he aged up to his natural years. The result is the same, though: now that he’s too old and frail to be Captain America, he trusts Sam to follow on in his stead. In the comics, Sam was humbled and felt the responsibility of taking on the mantle. Anthony Mackie’s character acts much the same way when he’s handed the shield.
Avengers: Endgame‘s final scene calls the upcoming Disney Plus series into question, though, as the title Falcon and Winter Soldier rather suggests it’ll follow Sam as Falcon rather than Cap. As such, it’s likely it’s going to be a prequel.