Why doesn't Canada have the same battles over affirmative action?

Simple: the Charter says that its Equal Protection provision "does not preclude any law, program or activity that has as its object the amelioration of conditions of disadvantaged individuals or groups including those that are disadvantaged because of race, national or ethnic origin, colour, religion, sex, age or mental or physical disability."

It's litigated around the margins, but the basic premise of AA is firmly entrenched.