The world and European champions have suffered a string of injuries which have contributed to their slight dip in form over recent weeks.
Carles Puyol's away goal in the 1-1 draw from the first leg last week gives Barca a slight edge against a team who have always made life tough for them.
"We play 11 against 11, there will be seven substitutes on the bench, and we are doing well," Guardiola told a news conference on Tuesday when asked about his possible team selection.
"It will be a game for men, it will be very demanding, and we'll need everyone to be at 100 percent."
Spanish internationals Andres Iniesta and Pedro returned to training with the rest of the squad after injury on Monday, although they took part in only part of the session.
Playmaker Xavi was surprisingly rested for their last two matches, including the first leg last week, while Chile forward Alexis Sanchez has been struggling with a shoulder problem.
Midfielder Sergio Busquets needed stitches in a gashed knee after Saturday's 2-1 league win over Real Sociedad while Ibrahim Afellay and David Villa are long-term injury victims.
"The most doubtful of the players is Busquets," Guardiola added. "Xavi is fine and Alexis is OK although he is still suffering a little.
"They have trained pretty well, we'll see how they are tomorrow."
Valencia coach Unai Emery, asked about Barca's cagey handling of injury news recently, replied: "It's a good strategy not to let on anything to your rival. If we knew, would it be an advantage?"
Barcelona are seeking their third final appearance in four years, and a possible 14th title since Guardiola took the helm in 2008.
"If we don't make it, we remain alive in two competitions," Guardiola said. "We have a chance to play our fourth final this season and the players are aware of that.
"The quarters and semis have been very tough but we have responded in an extraordinary way."
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