My impression from reviews is that Nikon's equivalents to the EF 16-35mm f/2.8 (the 17-35mm f/2.

and EF 17-40mm f/4 (the 16–35 mm f/4 VR) do not have the kind of advantage which would make people switch to Nikon, or prefer it in the first place.
Though the 16-35 & 17-40 would benefit from an upgrade, IMHO Canon's priority would be a lens to compete with the 14-24mm.