If you are not scared of a manual lens, you should consider the Samyang 14mm 2.8, it offers exceptional image and build quality and is dirt cheap compared to the few competitors. Mind that it has strange contortions so you probably want to use Photoshop or Lightroom with the lens correction profiles available through Adobes Profile Downloader. Just an idea even if you were looking for some mm more.
The Samyang 14mm is great lens at a ridiculous price; great built quality, very good IQ (espicially at f/5.6), low and easily correctable CA. The biggest downfall is the distortion, but it is not than bad for landscape, though it can be a problem if you are more into architecture (or shooting brick walls
I personally don't see a problem in the fact that it is a manual focus lens; using the hyperfocal, you can nail perfect focus every time with such a wide lens.
IMO, this lens is a fabulous lens, especially rather put the 2000$ price difference with the Canon alternative on something else (lens, body, food, car, etc