if the director didn't play two roles, that shoule be better!

I don't think that you've understood the meaning of why Robert Lepage played the two roles. In the play "La Face cachée de la Lune", Robert Lepage acted all the characters. The cast refers to the play, to keep a little of the original presentation. It also has a psychological aspect, for it makes a link between the two characters.

AL

I actually didn't first notice he was playing them both, only after the sauna-scene!

So I had no trouble thinking them as characters of their own.