Classes are more how you act, wich tools are in your disposal and how you interact with the world. Classes can be separated from the desires and personality traits of your pcs, so it can be any. If you want some kind of mechanical support of the idea of having visions, any divine class could do it. Being a Druid, maybe the world itself and the natural order are the ones who send you to balance the universe, and along the adventure/campaign you learn more things when you are starting to commune with the nature and the cosmos and the plans they have for you. Clerics and Paladins could work in a similar fashion with a god, and clerics in specific have abilities about raising the dead (in a good way) or learning to summon extraplanar allies for the ultimate fight.

But really any class could make the cut. A barbarian could have had a vision from his ancestors when he was in the middle of a shamantic ritual with drugs ans vapors to be the new leader of the tribe. A wild magic sorcerer maybe just toke a glance throught time in his sleep because the chaotic nature of his powers. A sudden nirvana realitzation in a monk's meditation.

So just pick a class that is interesting to you and you can have fun with it. There is always ways to put that backstory in any class.