Aguero, 31, has been in the first XI for three of Argentina's four games at the tournament, scoring one goal and setting up two in a front three including Lionel Messi and Lautaro Martinez in wins over Qatar and Venezuela.
Amid some doubts over the Manchester City star's place in the starting XI for the blockbuster clash at Estadio Mineirao, Aguero's spot was the only one Scaloni would confirm on in a press conference ahead of the match.
"What I can confirm is that Aguero is going to be a starter," Scaloni said.
"It always comes out that the doubt is Aguero and he ends up playing."
The Argentine boss then joked about the selection situation of Lionel Messi - with the superstar forward failing to reach top form with only one goal in his four matches.
"The rest is not confirmed, not even Messi," a laughing Scaloni added.
Argentina must turn around a poor record away to Brazil, who are tournament hosts and arguably favourites, if they are to reach the final of South America's football championship.
The Selecao have never lost a competitive game at home to Argentina, winning eight and drawing two.
Scaloni believes Tite's side, who scraped past Paraguay on penalties in the quarter-finals, are favourites to win the Copa America.
"They are in an important situation. They have been playing together for a long time, the coach has been [in charge] for a long time. That is an advantage for them," he said.
"Brazil are the favourites for the Copa, the rival that everyone wants to beat."
Their opponents Brazil haven't clinched the honour since a 2007 triumph in Venezuela.