Using oil in cooking is a big issue and concern
for many people - concerning the fat and cholesterol contents
of cooking oil. I was recently asked why Stir-frying needs
cooking oil, and the health effects. I won't discuss why
you need cooking oil for stir-frying,
read about it in this article. But I am going to tell
you about cooking oils - the best cooking oil you can use,
for flavor and health. So what is the best cooking oil?
This is a debatable subject. One of the better oils to use overall would have to be Olive oil. However, we're concerned about Canola oil here.
Olive oil has an excellent fat composition. Canola oil also appears to have a very good fat composition as well - it comtains 55% monounsaturated fatty acid; oleic acid, 25% linoleic acid and 10% alpha-linolenate, and only 4% of the saturated fatty acids (SFAs) that have been implicated as factors in hypercholesterolemia.  However, the health benefits or disadvantages of Canola oil is rather hotly debated, and there are some conflicting evidence from scientific studies in this regard.
Why Use Canola Oil for Cooking
When you hear the term cooking oil, you usually associate
it with fats and cholesterol, and you're right. But did
you know there are 3 types of fats? 2 of which are actually
good for your health. Read
about fat facts and types of fats in this article.
Looking at canola oil, it appears to be a healthy cooking oil based on its fat composition as we've already mentioned above - containing only 4% saturated fatty acids. There are 3 types of fats: saturated,
monounsaturated, and polyunsaturated... and 2 of the 3 types
of fats are actually 'healthy' fats, and they're actually
helpful to your health. Saturated fats is the bad type you
want to avoid. The other two types actually help control
the level of cholesterol. 55% of canola oil is monounsaturated. Based on these ratios, canola oil indeed has a good fat composition.
However, on the other hand, there are some studies - done on rats - that have found Canola oil to have certain adverse health effects such as causing hyperlipidemic (high levels of lipid in the blood) conditions in the test rats. In a rat study where the rats were either given a canola oil or soybean oil, it was found that the canola oil induces a hyperlipidemic condition. 
Another study also using stroke prone rats found that rats fed canola oil had a shorter lifespan compared to soybean oil fed rats (62 days vs 68 days +- 3days). The canola fed rats also had high blood pressure suggesting that it promotes hypertension, which is likely related to the shorter lifespan of the canola oil fed rats. 
These studies do not speak well for Canola oil; however, please keep in mind that theses studies were performed on rats and not real human subjects. Another study titled "Food safety and health effects of canola oil" stated that:
It [canola oil] is expressed from a cultivar of rapeseed that was selectively bred from old varieties in Canada to be very low in erucic acid--a fatty acid suspected to have pathogenic potential in diets high in the original rapeseed oil in experimental animals. Canola oil is free of those problems. It is the most widely consumed food oil in Canada, and has been approved for Generally Recognized as Safe (GRAS) status by the Food and Drug Administration (FDA) of the United States Department of Health and Human Services. 
1. J Am Coll Nutr. 1989 Oct;8(5):360-75.
Food safety and health effects of canola oil.
Dupont J, White PJ, Johnston KM, Heggtveit HA, McDonald BE, Grundy SM, Bonanome A.
2. Food Chem Toxicol. 2008 Jul;46(7):2573-9. Epub 2008 Apr 22.
Different effects of 26-week dietary intake of rapeseed oil and soybean oil on plasma lipid levels, glucose-6-phosphate dehydrogenase activity and cyclooxygenase-2 expression in spontaneously hypertensive rats.
Ohara N, Kasama K, Naito Y, Nagata T, Saito Y, Kuwagata M, Okuyama H.
3. Toxicology. 2003 May 3;187(2-3):205-16.
Rapeseed oil ingestion and exacerbation of hypertension-related conditions in stroke prone spontaneously hypertensive rats.
Naito Y, Nagata T, Takano Y, Nagatsu T, Ohara N.