None of the Canon offerings have equal edge sharpness like the Nikon. It's just something Canon seems unable to figure out.
Yes, although 16-35 and 17-40 are fantastic, 14-24 from Nikon seems a step above them. I think both those lenses have quite a bit of overlaps with the 24-70 and 24-105. A 2mm (~14%) difference is huge in wide angles. I think if Canon goes to 12-24 mm it will not overlap with its other two brethren.
May be my perceptions are incorrect, but Canon's wide angle lenses, especially at edges, need some more improvement compared to its telephoto lenses, which are really high quality.