Why is this a problem? Most religious Bible-type books I'm familiar with only mention the creation of "the" Universe--they never mention any others. Our Bibles only talk about God's creation of this Universe. So it's entirely possible--and acceptable to most religions on Earth--for there to be other Universes with other Gods.
This completely misses the point of theism as it is understood by most monotheists. God, on their view, isn't just a being who happens to exist and who happens to have created the universe around us. He is
existence itself. He is not simply the author of the universe but what makes even the theoretical existence of a universe possible in the first place. Even if no universe existed, the mere possibility of the universe - and of every possible universe - would exist solely as an idea in his mind.
Everything that exists does so solely because he created it and because he makes sheer existence possible in the first place; and
everything that doesn't exist but is merely possible is possible only because he exists. This is part of what theists are trying to get at when they say that God is the one necessary being, the one thing that simply has to exist irrespective of whether anything else does.
So Leibniz (this is in his
Theodicy Essays II 225 if you want to know):
Leibniz said:
The infinity of possibles, however great it may be, is no greater than that of the wisdom of God, who knows all possibles. One may even say that if this wisdom does not exceed the possibles extensively, since the objects of the understanding cannot go beyond the possible, which in a sense is alone intelligible, it exceeds them intensively, by reason of the infinitely infinite combinations it makes thereof, and its many deliberations concerning them. The wisdom of God, not content with embracing all the possibles, penetrates them, compares them, weighs them one against the other, to estimate their degrees of perfection or imperfection, the strong and the weak, the good and the evil. It goes even beyond the finite combinations, it makes of them an infinity of infinites, that is to say, an infinity of possible sequences of the universe, each of which contains an infinity of creatures. By this means the divine Wisdom distributes all the possibles it had already contemplated separately, into so many universal systems which it further compares the one with the other. The result of all these comparisons and deliberations is the choice of the best from among all these possible systems, which wisdom makes in order to satisfy goodness completely; and such is precisely the plan of the universe as it is. Moreover, all these operations of the divine understanding, although they have among them an order and a priority of nature, always take place together, no priority of time existing among them.
On this view, God is quite literally the
sum total of all possibilities. That means all actual things (including all things in all universes that actually exist) as well as all non-actual but possible things (including all things that do not actually exist but which could). There is more to God than that, of course, or we'd just have a form of pantheism, but the point is that God is what makes all these actuals and possibles actual
and possible in the first place. Indeed Leibniz constructs an argument for God's existence from this view, along the lines of: for possibles to
be possible, they must exist in logical space; but possibles
are possible; therefore logical space exists, and this is God. The important thing, however, is that God is the basis, as it were, for all possible combinations of things and events - not merely the ones that occur in our universe, but those that occur in any other universes that exist, and also the infinite universes which could have existed but don't.
So whether there are many universes or only one is really irrelevant. All existing things, no matter what universe they are in, exist only because of the one God. There cannot possibly be more than one God even if they are separated away in different universes, any more than there can be more than one of "the number three" (this is not to say that God is abstract in the way that a number is, though). God is not
inside this universe or any other, he stands outside and beyond and beneath them all. So on the assumption of many universes, the notion that God is somehow limited to this universe and has counterparts in other universes would be completely unacceptable to classical theism. I doubt, at the very least, you'll find many Christians willing to countenance the idea.