I don't know so much that there's no gods, but at the very least they generally aren't active in the way that D&D gods are.
In Ravnica, the published setting, the primary organized religion of the city-plane is the one maintained by the
Orzhov Syndicate. However, that organization is one part religion, one part bank, one part debtors prison, and one part organized crime. As far as I'm aware, there's no actual deity. There is evidence of gods existing, but they seem to be
more along the lines of cosmic horrors or demons.
The
Selesnya Conclave also operates temples and has some vaguely religious things going on, but they're very loosely organized in the way that druids often are.
The other white-linked guilds, the
Azorius Senate and
Boros Legion, act as the city's government and armed forces, respectively. There are creatures in these guilds which would be categorized as celestials in D&D (Angels in the Boros Legion, for example) but there's no religion involved.
There are several characters throughout the game that could be classified as demi-gods, particularly any Planeswalker character before
the Great Mending, primarily Urza, but also Serra and Freyalise.
Yawgmoth is another powerful character. Another would be
Avacyn, the Archangel. All of these characters have long since died, as far as I'm aware, however. Magic tends to kill off the main characters on most planes they visit. Magic also has
Eldrazi on the deity power level scale, which are much more literal Cthulu monsters.
Frankly, given the power scale that some characters reach in Magic, I would assume that
actual deities in the multiverse of Magic's settings would be more along the lines of the deities in Marvel (The One Above All or Love/Chaos/Order) and DC comics (The Presence). Unfathomable, unknowable, and, for all intents and purposes, omnipotent and omniscient. Gods that actually appear in Magic storylines or featured as cards are probably best described in D&D terms as demi-gods. Actual gods are not featured on cards simply because planeswalkers have no control over them whatsoever.