See the comparison here! I hope it helps you make a decision one way or another. More to come.
Tamron SP 24-70mm F/2.8 Di VC USD versus Canon EF 24-70mm F/2.8L USM versus Canon EF 24-105mm F/4.0L IS USM: Part I
Tamron SP 24-70mm F/2.8 Di VC USD versus Canon EF 24-70mm F/2.8L USM versus Canon EF 24-105mm F/4.0L IS USM: Part I