I'm sure Cruz has an explanation. Or if not he'll say something nasty about Trump instead of answering the question.
“Could Cruz honestly be given US citizenship because of his birth if both of his parents were Canadian citizens at the time?”
Under Canadian law the oath of allegiance required to become a Canadian citizen in 1970 was:
“I hereby renounce all allegiance and fidelity to any foreign sovereign or state of whom or which I may at this time be a subject or citizen.”
Under earlier United States law such a renouncing of U.S. citizenship could be used by the U.S. Government to find the person had indeed expatriated their U.S. citizenship. However, the lawyers and the U.S. Supreme Court saw fit to complicate and muddle the facts in Afroyim v. Rusk 1967(No. 456) 387 U.S. 253 by finding the 14th Amendment did not allow the cancellation of naturalized U.S. citizenship without certain formal affirmative steps being taken to do so before a State Department official. Consequently, even if Eleanor did renounce her U.S. citizenship to become a Canadian citizen, the U.S. Supreme court may find the precedent cases did not allow cancellation of citizenship or expatriation without further events taking place to formally affirm the expatriation. However, any inheritance of U.S. citizenship from a U.S. citizen mother could do no more than provide naturalized U.S. citizenship to a child born in Canada.