The Naturalization Act of 1790 probably constitutes the most significant evidence available. Congress enacted this legislation just three years after the drafting of the Constitution, and many of those who voted on it had participated in the Constitutional Convention. The act provided that “children of citizens of the United States, that may be born beyond the sea, or out of the limits of the United States, shall be considered as natural-born citizens.”
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The Act stipulated “children of citizens”. It takes two.
You raise a good point. The plural "citizens" implies that both parents would have had to have been citizens for the child to be automatically considered a "natural born citizen".
Per NPR, Cruz's father did not become a US citizen until 2005, meaning that, at the time of Cruz's birth in Canada, he only had one parent being a US citizen.