In the semi-finals, Real Madrid beat Atletico Madrid 5-3, while Barcelona beat Osasuna 2-0.
I think when they know they're going to face each other in the final, they'll prepare as well as they can, because we know it's always a very prestigious encounter.
The supporters will also be happy with this match and hope that the club they support will be the winner and lift the trophy. For now, I'm going with Real Madrid as the favorite with their better performances than Barcelona.
It turns out that this game will be the first in history when the champion plays in the final against the Cup winner, quite funny considering that Real and Barcelona historically collect 90% of the titles in Spain and it would seem that the likelihood of such a final should be very high.
By the way, do not forget that the Barcelona management set an ultimatum for Xavi (at least two titles this season), so for him this game will be vital since he cannot count on winning other tournaments.