The striker signed an extension with the club until 2018 on Monday after firing 12 goals in all competitions this season, including three in the cup already.
He now aims to fire Espanyol to their first cup final since 2006, and a potential clash with city rivals Barcelona - should the latter overcome Villarreal.
Victor Sanchez gave Sergio Gonzalez's side a vital away goal in the first leg with Bilbao, which finished 1-1, and Stuani hopes he can take centre stage to fire Espanyol through at home.
"I hope we can have a double celebration on Wednesday," he said. "This will be a momentous game and I'm looking forward to playing in it and winning.
"For us it's not just a semi-final, it's a final. It’s a massive game for Espanyol and all the people connected with the club.
"As players we are aware of what's at stake and we'll be giving 100 per cent against Athletic. The away goal gives us a slight advantage but it will be important to remain focused and try to score.
"This is a game we have to win."
Espanyol have won two of their three fixtures since the first leg on February 11, while Bilbao suffered a setback when exiting the UEFA Europa League at the hands of Torino last week.
The Basque side put that disappointment behind them with a 1-0 win over Eibar in La Liga on Sunday, and defender Andoni Iraola hopes Bilbao's packed schedule does not prove detrimental.
"Coming from a series of games is not ideal," he said. "We struggled to get here, but to play in a cup final is precious and we will try to take advantage.
"We know our opponents have an advantage, perhaps they are more focused because they have more time to prepare, but our desire to win will be more than theirs.
"Getting to a cup final is of such importance that our motivation will be high. An away goal is mandatory, so the stronger we are at the back the easier it will be to take risks in attack."
Ernesto Valverde has no new injury worries ahead of the match with Ander Iturraspe (knee) and Unai Bustinza (hamstring) both still on the sidelines.
Espanyol welcome back defender Javi Lopez following his recent suspension.
‘After Manchester City’s recent form, maybe they’re the underdogs against Manchester United!’ Former Red Devils defender on this weekend’s derby
‘Arteta, Alonso, Emery, me… none of us were physical players – we needed the understanding of the game. That probably helped us move into management’: Premier League boss reveals reasons for natural career progression
