We have something called the "Notwithstanding clause" in our constitution which basically allows the government to overturn any decision made by the Supreme Court. I don't think it has ever been used (but I could be wrong) because it might have negative political consequences for the party that uses it. Harper denies any plans to use the notwithstanding clause to overturn the decision to allow gay marriages, but many suspect he will if his party has enough support.
During one of the debates before the election Paul Martin challenged Stephen Harper to remove the notwithstanding clause from the constitution if he won, and he would do the same if the Liberals won. Harper more or less brushed off the challenge.