Argentina international Aguero has been absent for the past month after sustaining a hamstring injury in January's 5-1 victory over Tottenham in the Premier League.
However, the striker - who has 26 goals in all competitions this season - returns to provide a timely boost for manager Manuel Pellegrini, as City look to claim the first major trophy of the season against Sunderland at Wembley on Sunday.
The Chilean will be without Jovetic and Nastasic, however, the former has been struggling with a hamstring injury while the latter is out with a knee complaint.
"Jovetic and Nastasic are both injured," Pellegrini said. "They cannot play on Sunday. The rest of the squad is OK.
"I think it is very important for the team to have Sergio with us again because he is a very important player.
"We must see if he is 100 per cent fit to play the whole match. I must decide tomorrow and see the way he is recovering from the work from this week."
Victory for City would mark Pellegrini's maiden trophy in English football, but he is wary of the threat posed by Premier League strugglers Sunderland - who have already beaten Chelsea and Manchester United in the competition.
Sunderland have also recorded home victories in each of the last four Premier League campaigns to ensure Pellegrini takes nothing for granted.
"I will be very happy if we achieve it because I think it reflects all your hard work from the year," he added.
"I think we have played very well in the Capital One Cup because we won all our games, scored 19 goals and conceded just one. I think it is very important to win the cup.
"It is always dangerous to play against any team. Sunderland also have a lot of motivation to win, exactly the same as we do.
"Maybe we are the favourites but we cannot forget that Sunderland eliminated Chelsea and Manchester United, big teams. They are defiant. I am sure it will be a very close game."
