All I can predict is that a lot of people will answer who have never shot a Tamron, or possibly even this Canon, but who will confidently assert the Canon's clear, unmistakable superiority. And that FF sensors cost Canon $1000 to make.
But then again, in the spirit of full disclosure, I have only tried the previous Tamron version of 70-200 once, and it was in a camera store. All I could glean from that was the Tamron's AF was not quite as whisper-smooth as the Canon's, though not at all bad really. Photos of the inside of the store, viewed in the camera viewfinder, do not qualify me to tell you anything about IQ.
Presumably this new version is better somehow.