Can't really comment on the Canons as I have only seen their specs and online footage. However, I don't think the Sony CX900 is one of Sony's greatest camcorders IQ-wise despite what the specs say. Yes, it along with it's sibling, the AX100, has excellent build and great overall manual control for a rather compact form factor camcoder but based on my experience seeing actual footage at 1080/25 and 50p (XAVC-S) from the camera, the IQ disappointed me. I have also tested the exact same 1080p modes on my working AX100E and no surprise it gave identical results. What's wrong with them? First the footage in bright daylight is not very clean. Not that it had any noise but there was a surprised amount of aliasing in the image. And when examined closely on the monitors (with normal playback) the detail and resolution weren't that great either. I would say the level of detail and freedom from aliasing in the footage were even a bit behind those from a few cheaper palm-sized Handycams from Sony in the previous generations such as the PJ790V, PJ/CX760V or even CX700/560V.
If I were you I would shell out a little more for the AX100, shoot solely at 4K and downscale the footage in post, which will yield the best IQ for 1080/24,25,30p. If 60p and long zoom range are important then it could be either of the Canons.