Either Cruz has been a naturalized citizen since birth, when his mother registered his birth with American consul in Canada, or since his father became a naturalized citizen — or else he is not a citizen at all. He didn’t just automatically become a US citizen by giving up his Canadian citizenship. There is a process that all foreigners have to go through to become US citizens, including Canadians.
Since Cruz has a US passport, he is a US citizen. You cannot get a passport without proving your citizenship, which means since his birth certificate showed a Canadian birth, he had to submit proof that he had been naturalized at some point.
Cruz is most definitely a US Citizen, but he is naturalized, not natural born, and not even native born. His candidacy, like Obama’s, was founded on a lie.
Cruz did not go through the naturalization process. He was a citizen at birth, but we could quarrel over “natural born”.