I dug out an old but good book by Gottfried Martin, Kant’s Metaphysics and Theory of Science, and decided to read it again in the light of all the present discussions of Kant and his ontology. I think it’s a shame that this book is so hard to find, it came out in 1955 and I think it certainly deserves a good paperback reissue. Martin opens with a discussion of Leibniz and especially the idea of God:
The being of Euclidean space thus consists primarily in its being thought without contradiction by God. The presupposition that God thinks all possible worlds is also the ground for the possibility of physics. If all possible worlds and among them this world, are continuously thought by God, the being of the world is primarily a being thought and the world is therefore in its original being intelligible, transparent to reason. 
Martin argues that the brilliance of Leibniz consists in his ability to pick the leading ideas from other philosophical systems and this one comes form Malebranche’s notion that we see all things in God. Leibniz attempts to ground a kind of universal science, attempt that Hegel later dismisses as a “metaphysical novel” – why start off a book on Kant with God and Leibniz? Martin cites the end of Kant’s essay “On a discovery whereby any new critique of pure reason is to be made superfluous by an older one” from1790 – the essay that I have not read in a while, but I think it might be worth another look:
In this way, then, the Critique of Pure Reason might well be the true apology for Leibniz, even against those of his disciples who heap praises upon him that do him no honor; as it may also be for sundry older philosophers, whom many an historian of philosophy – for all the praise he bestows on them – still has talking utter nonsense; whose intention he does not divine, in that he neglects the key to all accounts of what pure reason produces from mere concepts, the critique of reason itself (as the common source of all them), and in examining the words they spoke, cannot see what they had wanted to say. [8:250]
Of course, Kant sees his task of the critique of pure reason as a continuation of the philosophical tradition, but that he would see it also as a true development of Leibniz is something that I think is worth thinking about it, only if a bit randomly today. I’d have to come back to this one later.