Read some more info from PCGamer, looks like it's going to be like the Marvel Ultimate Alliance Series:
Marvel's Avengers game will feature 'continuous single-player and co-operative gameplay',Up to four players can team up in the Avengers game, and customize their favorite superheroes to their play styles, according to the listing.
"Embrace your powers and join key members of the development team at Crystal Dynamics and the creative team at Marvel Games as they talk exclusively about the upcoming Marvel’s Avengers. This is the defining Avengers gaming experience: an epic action-adventure that combines cinematic storytelling with continuous single-player and co-operative gameplay. Moderated by Andrea Rene, assemble in teams up to four players, master extraordinary abilities, customize your heroes to fit your playstyle, and combine powers to defend an ever-expanding world under constant threat."
Square Enix will reveal the first gameplay for Marvel’s Avengers during its presentation at the Marvel Games Panel at San Diego Comic-Con 2019 on July 18 at 1:30 p.m. PT / 4:30 p.m. ET, the company announced.
The panel will feature Crystal Dynamics creative director Shaun Escayg and the performance cast of Marvel’s Avengers.
A live stream for the panel has not been announced, but the press release states that the gameplay premiere will be for attendees only. At this time, it is unknown whether Square Enix plans to share the footage online after the panel concludes.