Hundreds of recipes for brownies exist. You can find fudgy, chewy and cake-y versions, but most classic versions contain some combination of chocolate, sugar and butter. Brownie mixes, though, usually require the addition of vegetable oil along with eggs and water. If you prefer to use canola oil, or that's all you have on hand, your brownies will still come out irresistible.
Canola oil comes from the rapeseed plant; its name derives from the primary country that produces it: Canada. This oil is neutral in flavor, just like vegetable oil. Although it's lower in saturated fats than vegetable oil, you won't detect this in the flavor or texture of your brownie.
Substitute canola oil measure for measure for vegetable oil in a brownie mix or recipe. For example, a typical box mix making 20 brownies might call for 1/2 cup of vegetable -- or in your case, canola -- oil.
Concerns with substituting oils in a recipe come down to smoke point, or the temperature at which an oil burns, and flavor. Because canola oil has a smoke point appropriate for temperatures used for baking brownies and no distinct flavor, it's a good substitute.