You might be surprised how good the 28-300 is. Of course it can't possibly be as good as a prime or a smaller-range zoom, but they didn't put that "L" on it for nothing.They do...
Canon EF 28-300mm f3.5-5.6 L IS USM Lens
however I wont be buying one. Since any lens with more than 3x zoom suffers massively from IQ problems. Its a laws of physics trade off between quality and zoom flexibility.
It is. It's about the same size as the 100-400, but a tad heavier.The nikkon lens isnt very big at all, seems a perfect walkabout one, the canon L lens looks HUGE.