According to sources, the Captain America sequel will be closely linked to the characters in S.H.I.E.L.D.

Press release:

The second installment will pick-up where the highly anticipated Marvel’s The Avengers (May 4, 2012) leaves off, as Steve Rogers continues his affiliation with Nick Fury and S.H.I.E.L.D and struggles to embrace his role in the modern world.

It appears as though the next Captain America and S.H.I.E.L.D. movie are one in the same. From the press release we see that Steve Rogers will jump right from where The Avengers left off and he’ll most likely continue working closely with/for Nick Fury (Sam Jackson).

There’s rumors that Black Widow and Hawkeye will also be involved in the Captain America sequel and will most likely result in a romantic plot branch. The studio hopes that this will help increase the box office appeal of the film, as it’s the lesser known sequel compared to Iron Man 3 and Thor 2, which come out in 2013.

Source: ScreenRant