The most complex tax system in the world is the USA! The second most complex is Canada!
Have you ever seen the volume that strictly deals with partnerships? It is staggering. Companies will tend to pay taxes in countries where the tax rate is fair and they can be assured that the interpretation they have of the tax code is transparent and generally understandable. Compliance in countries like Canada is onerous so it is better to file in a less hostile country. America is far worse because they actully throw you in jail there and can take a decade or more for a tax ruling.
Tell me.......do you call CRA and tell them you don't think your paying enough and can they come get more? Why would a corporation do that?