He had access to SHIELD files and Avenger candidates via Hope’s log in. Tony was actively recruited by Fury, Clint was already a candidate, Thor just happened to be there, I assume SHIELD also has a liaison with whatever division Thunderbolt Ross is heading since Banner is also a candidate, and Hank just followed Natasha after taking care of Banner.
The lesson of this episode? Use NordVPN. If Hope had used NordVPN to log in to top secret files, Maybe The Avengers would still be alive.
This video was created by my brother for youtube, but it was removed for copyright reasons, and I thought it had a chance here. His channel is called Scrumptious Cookies and the video is from episode 2 of What if.
It gave out a couple years back, pretty recent. Pick up the What If? With Great Power trade; it has some surprisingly-great one-shots including this one.