From my observation, it is possible that Barcelona may use their first squad, but they might not put in full energy to play the match, as they have already won the La Liga trophy. It is also possible that they won’t use their full squad, and if that is the case, I will say that it makes the match easier for Bilbao. But let’s see what will happen, as football is unpredictable.
Barcelona has already secured the title, and Bilbao has already secured a place in the UCL. I think both teams have no motivation in that match. Barcelona will probably field their young players or even Barcelona B players. But on the other hand Bilbao also has no reason to play with high intensity. I predict Barcelona will still play most of their main squad but they will play without any pressure. Maybe Flick will make some substitutions to give the bench players a chance. The same thing seems to be done by Bilbao. I see that currently all teams in La Liga have already secured their positions for next season. Except for Celta Vigo who still have to fight for a UEL ticket with Rayo. And Leganes who still have a big chance to get out of the relegation zone.