A male female pair would be the natural choice but there is a chance that they might decide to breed at some point. Single pairs are less likely to breed then having multiple pairs.
A male/male pair can get a log just fine too.
There are no guarantees either way.
It is great that yours is still young, it makes it very likely they will get a long.
Also, the wonderful thing about caiques is that they don't tend to abandon their people in favor of another bird.