The Sigma 35/1.4 is optically a little bit better than the Canon. However, resale values on Canon L lenses are generally higher than 3rd party lenses (and if/when Canon releases a 35L II, its much higher price will likely drive UP used 35L prices, meaning you'll likely be able to sell a used 35L for more than you paid).
True about the resale value although I highly doubt that will be the case with the 35L, not with the sigma (and the fanbase it builds) around. There are people who would buy a canon lens just cause its canon but i doubt they'll be enough to stop the resale value from tumbling down even with a new lens announced.
Plus, for the sigma as a 3rd party lens, a 35 1.4 of this quality will keep its value for a long, long time. Actually given time i think sigma's price can only go up.