Boring guesses: In order of probability, Alonso, Russell, then Hamilton, with the latter two being closely matched, and Hamilton's form seeming to improve as Mercedes gets the car working.
Fun guesses: Leclerc, when the stars align such that on same day, the pit wall doesn't trip over its own shoelaces, Charles doesn't try to 11/10ths the car through an imaginary Mario Kart shortcut that's actually just an Armco, and Max has mechanical trouble, or Ocon, when the skies open up with torrential rain that red flags the race at just the right time in the pit stop cycle.
If the existing teams won't let Andretti Autosport join the grid, I can't imagine Hitech getting traction -- and if they did it'd make the Andretti snub even more insulting.