While the book is widely known for its take on the problem of evil, we're not in this discussion giving a sophisticated treatment of the historical arguments by Leibniz and others, as Voltaire certainly doesn't do this. In fact, he sees getting caught in the dialectical snares of such long-running historical debates as one of the chief problems to defeat in philosophy, and his choice of this mode of communication, the novel, is all about showing instead of telling. The Leibniz stand-in character in the novel, Pangloss, has a name that means "all talk" or "all tongue," whereas Voltaire wants us primarily to act, and he was known for his advocacy of anti-authoritarian social reforms.
His notorious attacks on religion are largely political: he was fighting for religious tolerance and against dogmatism (in favor of Newtonian science), not against Christianity as a whole, although he did have some things to say about the Judeo-Christian tradition that go towards explaining why he was a favorite of Nietzsche. He's also in the Phyrronian skeptical tradition, following Montaigne. Quoting from the Stanford Encyclopedia on his views in this respect:
Among the philosophical tendencies that Voltaire most deplored... were those that he associated most powerfully with Descartes who, he believed, began in skepticism but then left it behind in the name of some positive philosophical project designed to eradicate or resolve it. Such urges usually led to the production of what Voltaire liked to call “philosophical romances,” which is to say systematic accounts that overcome doubt by appealing to the imagination and its need for coherent explanations. Such explanations, Voltaire argued, are fictions, not philosophy, and the philosopher needs to recognize that very often the most philosophical explanation of all is to offer no explanation at all.
This is our second novel, after reading Herland last year. This serves as an excellent illustration of what Bergson had in mind by comedy, or more precisely "humor" which as the inverse of irony states what is in fact being done and pretends that this is what ought to be done; that's Pangloss's Leibnizian attempt to explain away the plentiful, obvious evil in the world and insisting that this rationally must be the best of all possible worlds, because God only does things with a purpose, and if we can't always see that purpose, it's only because we're too limited to do so. Voltaire instead wants us to accept that evil exists and work according to our meager capacities to overcome it, to "tend our garden."
You can also get it as a free audiobook via an Audible free trial (which will support PEL, of course). I've listened to samples of all the unabridged versions of Candide they offer (there are several), and like this one the best.
You might also want to look at this super-short story, "Plato's Dream" by Voltaire, which is reportedly one of the earliest sci-fi stories ever and directly addresses the question as to whether God's creation is any good.
Another short story of Voltaire's that I actually brought up in the discussion is his "Story of a Good Brahmin," which demonstrates why philosophy is sucky yet irresistible.