I have now watched the exchange between Harper and CBC reporter Terry Milewski a few times. Despite what Harper suggests, Milewski is not asking the Prime Minister to answer a hypothetical question. Rather, he is asking him to answer a simple legal question. To wit.; would he abide by the decision of the Governor General?
Harper's reply that he won't "reply to speculation," can be translated as Harper saying "I won't speculate on whether I will obey the law."
That is our Prime Minister. He is not willing to speculate on whether he will obey the law.