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I own both. They are different. Not sure I consider one better than the other. The 5D II seems somewhat less amenable to pushing the highlights around in post, but, on the other hand, seems to need highlight adjustment less.
BUT (and I consider this huge) different lenses seem to affect dynamic range more than the camera bodies do. If I shoot for instance at f/5.6 with the Canon 50 f/1.4 and the Zeiss 50 MP f/2.0, the Zeiss usually produces a wider histogram. Sometimes the Canon lens will not fill the histogram, while the Zeiss is knocking values off both ends on the same image. And the great part is that on the 5D II, Photoshop's RAW fill light function brings Zeiss shadow values back in range beautifully. That has somewhat changed the way I shoot, from exposing notably to the right previously, to trying just to fill the highlight side of the histogram on the right, and bringing the shadows up in post. Still experimenting, because I just got my Zeiss lenses, but that is what I am doing now.
Long story short: when you are looking at dynamic range, pay at least as much attention to your lenses as to your camera body.