Horses don't need Omega 6 fatty acid supplementation. Decent grass hay actually contains all they need, plus more, so there is no need to give them any oils or supplements that has Omega 6s, or much of them. You want to see Omega 3's much higher if there is any Omega 6's at all, like 3:1 or more.
Flax meal or oil is usually 3:1 or 4:1 Omega 3 to Omega 6 in values.
From what I can find, Canola oil is 23% omega–6, and 10–15% omega–3, which is about 2:1 or 1.5:1. That's not a good ratio for omega-6:omega-3 for horse diets. ALL ABOUT OILS
Canola oil contains an omega-6 to omega-3 ratio of 2:1. Flax oil is 0.3 to 1.
This may be "good" for people (as the article claims), but it flax is the healthier alternative for horses.
According to this chart, Sunflower seeds only contain trace amounts of Omega 3 fatty acids (which give better hoof/coat results than Omega 6), so the hoof/coat improvement we see from feed BOSS (Black Oil Sunflower Seeds) must come from the high amounts of Vitamin E. Omega-3, Omega-6 in Oils Nuts Seeds. Essential Fatty Acids
Here's a page with good information on BOSS, including a nutritional breakdown. I do not agree with feeding 1 lb of BOSS though. Horses' digestive systems are not meant to eat that much "seeds" at one time. I would be afraid of the risk of colic or choke. 1 cup per-feeding is all I would be comfortable feeding. Black Oil Sunflower Seeds for Horses
Another article giving some good "devils advocate" thinking on BOSS. Definitely worth reading. Black Oil Sunflowers (BOSS) for Horses