100–25600 ISO (expandable to H1 (51200), H2 (102400)), compared to 100–6400 ISO (expandable to H1 (12800), H2 (25600))
61 Point AF + 41 Crosstype AF compared to 9 Point AF + 6 Assist Points. The Mark III's autofocus system is inherited from the recently announced EOS-1D X, and marks the first time since the EOS-3 film SLR that Canon has put its top-of-the-line autofocus system in a non-1-series body.
6 frames per second continuous shooting compared to 3.9 frame/s
TTL, full aperture, 63 zones compared to TTL, full aperture, 35 zones
Silent, low vibration TTL shooting modes (single shot or 3 frames/s), compared to live-view-only silent shooting modes.
Larger 3.2-inch (81 mm) LCD with 3:2 aspect ratio, compared to 3.0-inch (76 mm) at 4:3. In turn, this means that the native still images of the Mk III completely fill the screen, while the Mk II's native images are displayed with a black border on the bottom of the LCD. Also, while HD video remains letterboxed on the Mk III LCD, as on the Mk II, the 3:2 ratio allows more of the screen to be used for video display.
Headphone-out to monitor audio, the previous one having none.
Dual card slots—one CompactFlash (CF) with full UDMA support, and one SD (including SDHC and SDXC cards, but does not exploit the UHS-I speed class). The Mk II has only one CF slot.
Canon issued a product advisory indicating that the camera's LCD panel, when illuminated, may impact the camera's light metering. Any camera bodies sold with the issue will be fixed by Canon free of charge, and any body shipped after the first week of May 2012 likely had the defect already rectified.