Copy and paste from bodybuilding.com
Canola is an industrial garbage oil, originally intended as a machine lubricant. It comes from an engineered form of rapeseed which has had its erucic acid (highly toxic and unpalatable) removed. The process of extracting the oil generates so much heat that it turns the canola rancid, which then requires a deodorization process.
Canola-
It is rapeseed stripped of euric acid.
It is considered by some docters as heart healthy because of the omega 3 content but the way its processed takes it above 500 degrees celsius which could mean that a large portion of the good fats are rancid. Its an extremely processed oil.
It's actually not that high in PUFA, and is in fact mostly MUFA like olive oil, but what PUFA's you're getting are rancid. Even fresh, healthy PUFAs from fish and nuts put you at some risk of oxidative tissue damage, but the fat from canola, corn, and soybean oil has already oxidized before it even enters your body. Canola is just overproduced industrial waste being peddled as cheap food.