I've been having some infinity focus AF trouble with my a7ii + Metabones T-smart mk4 adapter and Canon 17-40. I'm not too sure if that's a common phenomenon amongst fellow users but seems like its common enough to prompt Metabones to mention "AF accuracy improvement for subjects near infinity." for their latest V0.53 update.
Unfortunately I don't feel the issue has really been resolved and I'm not sure why either. The adapter works perfect on my sigma 50mm non-art and Canon 85mm on the other hand!
I'm liking the IBIS and the exposure latitude i get from the Sony RAW files but I'm not totally sold on the A7 series to make a complete switch to Sony, but i am considering the Sony 16-35 F4 or the Canon 6d2 when it is eventually released
I have not had any focusing issues with the Metabones and the 17-40L. That is my go to lens. Do you have a Canon body to test the lens on, to see if it is the lens?