The fine print states that only the 15W40 is 20% off. According to my calculations that's $1.40 a litre if you buy two jugs and get two rebates.
If it were 10W30 it would be a lot more tempting. You could actually use that in Southern Ontario year round. A great deal if you have a use for 15W40, that's the lowest price I have ever seen any oil at in Canada.