Well....guess that a dictatorship or at least a very "military hand" on the government would be on the cards for almost any Latin American country during the 1960s and 1970s....if, somehow, Goulart manages to avoid (or survive) 1964, the next potential crisis could be the 1965 presidential elections, which could turn very sour in most of the cases: the candidates would be, by the right, Carlos Lacerda (governor of Guanabara state), former president Juscelino Kubitschek ("JK") by a kind of "center" and by the left, either Goulart (in 1963-1964 there was discussions if Goulart could run for reelection due to its "abnormal" rise to power) or Brizola.
A last poll before the 1964 coup showed that, despite all internal crisis, electors were somewhat split between such three forces: Juscelino being the front-runner, with something between 20 to 50% of the votes depending of the city where the poll was held, followed by Lacerda between 15 to 20%. A specific question was made about the voting intentions on Goulart (if reelection was possible to him) resulting in a surprisingly 50% of positive answers. So, in a gross approximation, we could say the the 1965 could end in a trifecta between the three candidates, each one polarizing a part of the total electorate, without a clear majority.
As at that time, there was no ballotage or second run, odds are that a President would be elected in a close race without a clear margin and, to make things even more confuse, a great probability of the Vice-President (which was also directly elected) being from a distinct political matrix than the elected President.
From this, my guesses are, according to the elected president:
Juscelino elected: Being a centrist and a kind of eldery stateman, his election helps to stabilize somehow the country in the immediate period. However, there is no money or energy (in OTL JK discovered a protaste cancer in 1970 and records of heart issues since his first administration) to invest in new large projects. The result is a tepid government which, to end of the 1960s, seems old fashioned and disconnected with times, with previous electors moving either to more leftist approaches or, as a reaction to that, claiming for "law and order" by the right / military. In this scenario, where the left wing is more entrenched in the Brazilian society, a coup is averted until the 1970s, but probably would happen in a more drastic versions, more like OTL Argentina or Chile, in order to "clean" society from leftist ideas.
Lacerda elected: The "dream" candidate of the military, so no coup. The issue would be how to deal with the left and leftist populist movements, specially in a time where the idea of armed movements and guerrilas was gaining traction in the continent. So, a coup doesn't happens, but a kind of autoritarian administration, with exercise of exceptional powers could arise during Lacerda's tenure. By the end, could see something like OTL Bordaberry's Uruguay or even the early days of the civic-military dictatorship in this same country.
Goulart / Brizola: Coup before of just after the elections....
Basically LATAM was a hot bed for military coups during all the 1960s until (very) late 1970s.....very hard to imagine Brazil solving its right-left political dispute without the intervention of the military at some point during that period.
