Get Sigma DG HSM Art at B&H Photo.
I just bought the Sigma MC-11 Mount Converter/Lens Adapter to have around because it is $100 off; at $149 and free shipping it is useful to have around. I used one last year with the Canon 11-24mm f/4L on the Sony A7R II, for example.
BTW, my #1 wish for a lens I don’t have for Canon is the Canon EF 11-24mm f/4L. It just hasn’t made it into the budget yet. I love that 11mm to 15mm range; see Examples: Mt Conness Watershed and Beautiful Boulder at Four Focal Lengths. I’ll take it any day over the Sigma 12-24mm f/4 DG HSM Art, because the Sigma has wild field curvature.