Currently, Canon's widest zoom lens (excluding fisheye) is the EF 16-35mm f/2.8L II. There are rumors and perhaps sightings of prototype zoom lenses as wide as 12mm being tested. An f/4 model will save weight and cost over the f/2.8 version but Canon will still have to decide on the narrow end of the lens - perhaps 12-24mm? These are early days yet for another wide angled 'L' zoom. Canon needs to put out some of the more urgently required zooms, like the EF 100-400mm f/4-5.6L II and the EF 200-400mm f/4 L lenses.
I have the Canon EF 16-35mm f/2.8L II lens. It is my favorite wide angle zoom lens and goes into my equipment bag every time I go on a photo shoot. Visit my website MichaelDanielHo.com to see travel and landscape photos taken with this lens.