Sterling is prepared to delay talks on his contract, which runs out in 2020, until after the World Cup
Aguero joined City from Spanish side Atletico Madrid for a reported £38m in 2011 and has been linked with a return.
"We all want him (Sterling) to stay as long as possible," Guardiola said. "The chairman and myself want him to stay a long time."
Aguero is City's all-time top scorer and their top scorer this season with 30 goals in all competitions but in the past he has reportedly felt he was being forced out of the club by Guardiola.
"I think [returning to Atletico] is not going to happen - my desire is it will not happen but I don't know," Guardiola said.
"Sergio will stay until he decides his time here is over."