I have both the Sigma 85 1.4 and Canon 85 1.2 L. I know this isn't the comparison you are looking for, but thought it may be of some help.
Bottom line is...both lenses are brilliant. I have had the Sigma for longer, but have used the Canon enough to make a reasonable comparison. The Sigma is quicker to focus and has excellent bokeh at 1.4. I was lucky to find one without focusing issues - I adjusted the lens at first for back focusing, but soon put it back to zero realising it was user error rather than the lens. The Canon has a more three dimensional feel to the images, and I personally prefer the colour and saturation. I am still questioning whether it was worth the money for the Canon!
The Sigma is a lovely lens for the money, and a while ago I was in the same boat as you. I did a lot of research and decided the Sigma was the better choice over the Canon 1.8. I have used the Sigma for fashion, live bands and portrait photography and have been over the moon with the results. I also own the Sigma 50mm 1.4 - it doesn't get used unless I really need it, in my mind it doesn't compare to the Sigma 85mm.
Edit: See below.