Let's say that Harper doesn't become chief aide to Jim Hawke and continues working for Imperial Oil before moving to the States to work in an oil company there. That would probably place him in Texas.
This happens at about the same time that a repeal of the 22nd Amendment is passed towards the end of Reagan's second term. We'll say that initiative was part of a larger package of reforms to presidential eligibility requirements, including the requirement that candidates be born in the United States or to at least one US citizen.
We'll say that history goes on more or less as OTL from this point onwards, at least until Harper decides to run for elected office (if he does).
Does a Harper living in the United States decide to enter politics? Can he win elected office? Does he have a shot at the Presidency one day? If so, and he wins, how does he govern, and how different is America?
Without Harper on the Canadian scene, how do Canadian politics develop? Could somebody else have unified the Canadian right, or was Harper uniquely placed to do so and subsequently win a government?