I have developed my own recipes and I use canola oil almost exclusively in all my cakes (no butter, no shortening) because it yields a moister cake. You might want to try to check the ratio of your leavening to the flour. You have to be sure it is 1 tsp of baking powder per cup of flour used in the recipe (or if using baking soda – you need only 1/4 tsp soda per cup of flour. When recipes say to alternate flour and liquid when adding to the mixing bowl, I will add all the flour in at once, mix it slowly until the flour is incorporated, then add the liquid slowly, stopping and starting the mixer to let it incorporate. I do this because this lets the flour mix with the oil and get coated, thus preventing the gluten from developing too much. Just barely mix at the end until the flour and liquid (in my case, I amost always use buttermilk exclusively) are incorporated into the cake and then stop mixing, you are done.
Hope this helps – I learned this from a book called Bakewise which I know some people live by and others hate but it totally works for me and my clients love my cakes’ taste and texture. good luck.