I have an A7rII and I find I need a good wide angle zoom. For some reasons (*) I am quite interested in the Canon 16-35/4.
Unfortunately I have seen some tests indicating that the 16-35/4 does not work very well on the A7rII.
The first one was by Ken Rockwell: How well do Canon lenses work on the Sony A7R II with an adapter: Sony A7R II vs Canon 5DSR, now I don't trust Ken Rockwell very much, especially as he extrapolates from Leica M wideangles not working well on the Sony.
But, Tony Northrup made a direct comparison between the Canon 16-35/4 and the Sony 16-35/4. My take on that was that the Canon performed better than the Sony, except on the short end near edges corners. Also they found that the Canon lens was much sharper than the Sony at the centers.
On the other hand, I am pretty sure Stefan Steib finds that the 16-35/4 Canon is usable on the A7rII with his HCam Master TSII.
Now, it is easy to say "cower glass" but Sony has around 2 mm of cover glass, while Canon's seem to vary between 1.0 - 2.0 mm ( LensRentals.com - Sensor Stack Thickness: When Does It Matter? ). Now, cover glass makes for a difference, Lensrentals found in their tests of Sony FE-mount lenses that 2 mm yielded best results (they tested 0, 1, 2 and 3 mm), but the FE-mount lenses probably have the outlet pupil closer to the sensor than the Canon lenses.
I also have a Canon 24/3.5 TSELII lens, I have a sort of mixed experience with it on the Sony A7rII. Mostly it works well and I don't really see issues on resolution tests, but I find it doesn't work well on thing like tree tops.
My best friend has a Canon 5DIII and we have run some shots on the Canon 24/3.5 TSE LII when it arrived, and we found that it was not that great in the corners.
But this image was quite OK (it is stitched from two images with vertical shift):
Shooting the 24/3.5 TSE LII on the Sony I would say the results are a bit similar. Here are some samples, all on the Sony A7rII if not indicated otherwise:
Just to point out, DPReview did also test the Canon 24/3.5 TSE LII on Canon:
Hopefully we get some interesting feedback on this. Would be interesting for potential buyers of wide angles for the A7rII.
(*) The reasons I am interested in the Canon 16-35/4 over the Sony 16-35/4 is that it can be used on the HCam Master TSII I have. It is also less expensive than the Sony lens.