I guess Candide can be considered a heroic figure. He does rise to the occasion and kill Issachar when he has to do so, and the inquisitor as well. He certainly goes through enough adventures to be a hero, and where he goes, important things happen. That kind of focus of fate often marks a hero.
That said, I don't think it is that useful to think of Candide as a hero, because of the state of extreme innocence in which he starts the novel. He's so naïve that he's not really in the action for a lot of the first section. He's more of a dopey spectator.
I see the Candude as being less of a Hero and more of a traveller, on a journey. He gets wrapped into things like the above mentioned murder of Issachar. But I find it hard to wrap my mind around the idea that he a learner could be a Hero.
On the other hand he is obviously a proficient marksman from the sentence, "He could shoot a nut off a bush without touching a leaf." But skill with a fire arm alone does not make one a competent hero.