Usually if someone gives birth while on vacation or on a job working overseas that child is also considered a natural born citizen if the parents were U.S. citizens and they register the kid with the Embassy. So if Cruz was born in Canada, it probably boils down to if his parents were citizens. If so, I have no doubt like Goldwater the courts would rule him to be a natural born citizen who just happened to be born outside of the United States. The constitution does not specify birth has to take place in the U.S.
So let the courts decide. My guess is Cruz will be considered a natural born citizen if his parents were citizens at the time.