The dictatorship screwed over a lot of political careers, from mayors to governors to senators, so there are plenty of options to choose.
I'll throw in a few names:
Iris Rezende: mayor of Goiânia from 1966 to 1969. Could've become governor of Goiás in the 1970s and rise to higher offices from there.
Ronaldo Cunha Lima: mayor of Campina Grande (PB) for three months in 1969. Much like Rezende, he could've risen to the governorship of Paraíba in the 1970s.
Artur Virgílio Filho: senator from the state of Amazonas from 1963 to 1969. I personally doubt his chances, since he'll probably be eclipsed within PTB by people like Brizola and other gaúchos.
Badger da Silveira: governor of Rio de Janeiro from 1963 to 1964.
Gilberto Mestrinho: governor of Amazonas from 1959 to 1963, and after that a federal deputy until 1964.
Almino Afonso: federal deputy from Amazonas, served in Jango's cabinet for a few months in 1963.
Sereno Chaise: mayor of Porto Alegre from January to May 1964. Was a close friend and ally of Leonel Brizola.
Waldir Pires: almost became governor of Bahia in 1962, served in Jango's cabinet.
Rubens Paiva: federal deputy from São Paulo, took part in a congressional investigation on IBAD's shady connections. Was tortured and murdered in 1971.
João Doria Sr.: federal deputy from Bahia, a staunch nationalist. Pretty much diametrically opposed to his son's political profile.
Miguel Arraes: governor of Pernambuco from 1963 to 1964. He would've been a very strong candidate in 1970 and other presidential elections after that - his national profile was on the rise before the coup ruined everything.