I would argue for the existence of God simply due to the fact that nothing currently attributed to God is definitively impossible.

Several of the key things that have been attributed to God's supernatural abilities in the past have been, to some extent, replicated ourselves by technology.

We are, at current, able to prepare elements in a laboratory setting that do not, to our knowledge, exist in nature. Admittedly, this is not the same as creating matter from nothing, as we're merely assembling parts that already existed. But conceptually, this is certainly not impossible.

We've also demonstrated that the laws of conservation can be broken, albeit briefly and in a localized sense. Admittedly, this is not the same as calling all the matter in the universe into existence- but again, at the conceptual level, the small scale, certainly not impossible.

We've manipulated the genome of multiple organisms to create altogether new ones- some are hybrids, others are altogether new, able to reproduce, and fundamentally incompatible with their predecessors. Admittedly, this is not the same as creating new life from scratch- but again, at the conceptual level, certainly not impossible.

We can create and manipulate matter at the subatomic level. We can assemble elements, and also molecules that did not previously exist. All DNA is, is an extremely complex molecule. The ability to assemble DNA from scratch, while a staggering undertaking, is not beyond us by any stretch of the imagination.

Our technology is merely a set of tools designed to accomplish specific tasks; as such, given sufficient time, energy, et al, there is no reason to think that anything currently attributed to God is impossible. As such, the idea that God himself is impossible is a non sequitur.

I'll grant that I consider God, as presented in the Bible and many other works, is very unlikely given what we can see. But even that God has done nothing that we can demonstrate to be impossible.

To be fair, possible is not necessarily probable, and probable is not necessarily factual.

Edit: Predecessors. WTF is a Predessor anyway?

Well, being a Christian pretty much inherently requires that the Bible be treated as The word of God, and either entirely factual, or a mix of metaphors intended to teach and that which is factual.

Christians know Heaven is real because they are Christians. If they did not, then they pretty much wouldn't be- by definition.