Gotta say I was pretty sceptical of him back when he was at Valencia and was glad when we didn't go for him, but he's really stepped his game up at Juve and if Semedo really is intent on leaving Cancelo would be a great option to replace him. If Juve is willing to let him go, now that's another question. I doubt it though, he's been really good for them and I can totally see them simply keeping him if they don't get an extraordinary offer for him (at least 50M). And since we're not getting anywhere near that for Semedo, we would again be spending extra money, which is unacceptable.
Even if Semedo leaves though, I could see our Board simply promoting Wague (which I think will happen in any case) and just settling for Roberto and Wague, which would be pretty horrible, but I could totally see it happening with this Board and EV who plays Roberto every game he can anyway. If Sergi gets injured, he'll just play Wague then, otherwise it's Roberto all the way.