Actually out of all oil out there I'd prefer canola the most (outside of flax, of course), because it has the biggest (or at least one of the biggest) omega 3 to omega 6 ratio. I personally gave about a small cup/day in Summer and twice/day in Winter (I switched to flax meal since that).
It's great for young horses in training, really any horse being worked more then 2 days a week, it's not only helps their coats but helps their gut digest food better. I have always fed oil to my horses or horse I'm training. For a average size horse 1/2 cup, large draft about 1 to 1 1/2 for smaller horses and ponies 1/2 cup is just fine as well.