Half-Life:

Pedro Pascal as Gordon Freeman (Cranston's kinda too old for the role of Gordon) (He doesn't have to talk)

Merle Dandridge, the original actress for Alyx, as Alyx Vance (because the only other person I could think of was Mila Kunis, and that's a major NO)

Jake Gyllenhaal as Barney Calhoun

I think Idris Elba could work good as Eli as long as he doesn't use a deep voice since Eli's more laid back

Robert Patrick as The G-Man

Harry S Robins, The Original Dr. Kleiner, as Isaac Kleiner

Michelle Forbes, the original Dr. Mossman, as Judith Mossman

Jeff Daniels as Wallace Breen (R.I.P Robert Culp)

Louis Gossett Jr and Michael Shapiro should be in the cast too.

Portal:

Ellen Mclain, the original GLaDOS voice, as GLaDOS

Stephen Merchant, the original Wheatley voice, as Wheatley

J.K. Simmons, the original Cave Johnson, as Cave Johnson

Nolan North, the original SPAAAAAAAAAAAAAAAAACE! Core, as The Space Core

Paul Dano as Doug Rattman

And now there's a tie between Alésia Glidewell, the original model of Chell, or Chloe Bennet as Chell.

THIS TOOK ME ALL DAY, I'M BEING HELD CAPTIVE BY GORDON HIMSELF! SEND HELP!