In regards to allies for missions and how you can normally only take 1 ally, is it possible to take both R2 and 3PO at the same time or are you limited to only taking one or the other?

I ask because it specifies that you get both as "allies", making me think you have to choose, but it also seems strange that you can't take both at the same time.

If the rebels win Canyon Run (Twin Shadows), they get the "Counterparts" Reward Card:

"During setup of any mission, when deploying Rebel figures, return this card to the game box to deploy either R2-D2 (Loyal Astromech) or C-3PO (Human-Cyborg Relations) as an ally at no threat cost. This does not count against the 1 ally per mission limit."

Other than that, I don't think you can bring them both. Too bad that reward card is only good for one use. Although if you're playing the Twin Shadows mini-campaign, then you'd only need that card once.

Upto one ally, unless you have and spend Counterparts to bring either one of them in addition to the one selected ally.