Until there is scientific evidence, it's a philosophic question and not a scientific one. From many philosophic standpoints, it's a bit of a nonsense question.
The basic problem that you're likely to run into philosophically is that, regardless of whether the universe is a simulation, it is our universe. There's no reason to think that it being a simulation would have any consequence for us, or that it would be detectable. Even if you were to find some artifact of the simulation, it would be indistinguishable from a weird quirk in physics. You could argue, for example, that the reason quantum mechanics is indeterminate is that the simulation doesn't actually calculate the location at particles at the smallest level until that level of accuracy is needed. It's a neat idea, but indistinguishable from "That's just the way physics works."
If this were a simulation, we have no access out to the larger "real" world outside of it, including the "computer" running the simulation, and therefore would have no grounds to make assertions about what that world would look like or how the simulation should work. We have no reason to think this supposed "real world" contains people, or creatures anything like what we've imagined. This supposed world might have entirely different rules of physics. The simulation might run on a "computer" that is not a computer, and is unlike anything we understand. Not only do we not know about these things, but we have no reason to believe the tiniest scrap of information about the supposed world is discoverable.
If we were to assume that our universe is a simulation of a sort that we know about, we should guess that the only way we would discover this deeper truth would be a revelation made by its creator. For example, there's no possibility of a character in Grand Theft Auto to learn that he's in a video game unless the developer programs the character to know it. Without the intervention of the developer to make this information available, the GTA character would have no way of figuring out whether the game is running on an AMD processor or Intel.
So given that, even if we assume for the sake of argument that we are in a simulation, we have every reason to believe that we can never discover evidence of it, and our existence in the simulation is indistinguishable from what our existence would be if we existed in reality. It's a distinction without a difference. Our simulated universe is still as real to us as the real universe would be to us if we were real. The whole thing turns into a broader philosophic question of, "What if the nature of the universe is actually unlike anything we understand, or are capable of understanding, and everything we think we understand is illusory?" It's a somewhat interesting question to ponder for a few moments, but it makes no sense to try to answer it. If it's the case that we're incapable of understanding reality, then there's no further use for inquiry.