i re-watched it last night starting from the scene with brian/michael on catwalk.i paused several times, brian does have a good view of the crowd,& even when he has his back to the crowd,he does look over his shoulder eyeing all.So was he looking for justin cuz he suspected trble in paradise when he saw justin in the diner wearing the same clothes?
You are right when brian walks into the backroom,there is a very extremely subtle look when brian sees justin there.
I think also going back to 3-06 when justin is over at woodys sitting at the bar having a drink, i dont think he went looking for brian, but he expects him to be there, same as this scene too.