[3] On 2 August 2020, Viera made his debut in the Paraguayan Primera División in a 4–1 home win over Club Sportivo San Lorenzo, as a 66th-minute substitute for captain Mathías Villasanti.
[6] On 17 February 2023, starting by surprise away to Guaireña on the debut of new manager Facundo Sava, Viera scored his first goal for Cerro Porteño with a left-footed strike in a 2–0 win.
[7] In April, his sudden absence against Sportivo Ameliano caused rumours that the Argentine had dropped him, but he was in fact hospitalised after having been kicked in the genitals during the previous match against Tacuary.
[2] In the latter team, he helped them to the quarter finals of the 2019 FIFA U-17 World Cup in Brazil, giving two assists as they came from behind to beat neighbours Argentina 3–2 in the last 16; Spanish sports newspaper Marca named him one of eight stars of the round.
[12] Viera made his debut for the senior Paraguay national team on 6 September 2024 in a World Cup qualifier against Uruguay at the Estadio Centenario.