The Catalans giants are ready to extend Villa's contract as the striker is fine form while their defence need reinforcements and a long-term replacement for Carles Puyol could Borussia Dortmund's Mats Hummels.
In case Barcelona fail to keep Villa, their next target would be Aguero, who has been instrumental in City's title winning season. The Argentine is also a target for Real Madrid.
City are planning to offload a number of players in the summer including Carlos Tevez, Samir Nasri, Joleon Lescott, Edin Dzeko, Yaya Toure and Maicon. But the defending champions already have eyes on some of the biggest players in world football.
City could bid for Atletico Madrid striker Radamel Falcao and Napoli's Edinson Cavani while Luis Suarez is on their target list.
Meanwhile, Barcelona will listen to offers for striker Alexis Sanchez. Arsenal manager Arsene Wenger will consider signing the Chile international, who was also on Manchester United's radar before joining Barcelona.
However, Barca have been struggling at the back this season with Javier Mascherano established as a centre back alongside Gerard Pique. Barcelona will aim to bolster their defence with the signing of either Kompany or Hummels.