For Black Friday 2017, authorised Canon retailer Adorama has discounts on a huge set of Canon lenses, up to $550. The rebates are are made up from instant discounts and coupon code CAUJDQ3E1 (you enter it at checkout, and it’s only there you’ll see the final price). I made some tries and learned that the discount coming from the coupon code depends by the price of the lens. For instance, on the EF 16-35mm f/2.8L III you’ll get $199.90 discount from the coupon code, on the EF 11-24mm f/4L you get $269.90. The rebates from the coupon code add to the instant discounts. Take it while it lasts!
If you’re hunting deals it’s a good idea to regularly check the page of your interest.