Do humans have a brain or are we a brain that has a body

Brain that has a body.
Our body is just like this big machine that our brain lives in, in order to survive.
You can destroy most of the human body and the human stays alive, or you destroy the brain and the human is dead instantly.

Both, though we lean towards the latter. Our consciousness is the result of the electrical activity and physical structure of our brain. In other words, the mind is what the brain does. Alter the brain, and you alter the mind. Everything we know about neuroscience points to this strictly materialist model of the brain. Consciousness is an emergent property of the brain, and it is certainly greater than the sum of its parts, but it is still firmly rooted in the physical.

At the same time, our bodies affect our brains. Hormonal secretions, nutrients, ingested chemicals, and sensory input all affect how the brain functions. The brain would function very differently if it were simply kept alive in a jar. Still, that's where all the real action goes on, even if brain and body are, for the most part, inseparable.

I think it's more of union.

Or maybe that's what my brain tell the rest of me so my body won't rebel against it...!

Best question I have seen in a while :D

we have a brain
it is just one organ we evolved in the human body

Parts of ourselves do not 'have' one another. We are made up of many parts.