That said, although legal scholars can have how many angels can dance on the head of a pin debates about this, the most reasonable interpretation is probably that they're US citizens/eligible for US citizenship from birth. If push ever came to shove on this question, one would hope the courts would side with the most liberal interpretation.
"The candidate is a natural born citizen by virtue of being born in Canada to his mother who was a U.S. citizen at the time of his birth."
Place of birth does not matter for the House or Senate. Only need to be a US citizen.
For the President it's a "higher standard" you must be a native born Citizen.
Which isn't 100% defined and legal scholars can and do argue the edge cases based on lots of things including very old British common law antecedents. The consensus seems to equal citizen from birth although some disagree.
"No Person except a natural born Citizen ... shall be eligible to the Office of President"
Natural born means "citizen at birth", not "born in the US"> One can also be a citizen at birth (under certain circumstances) by having parent(s) who are U.S. citizens. Ted Cruz unequivocably meets this standard.
[0] https://en.wikipedia.org/wiki/Article_Two_of_the_United_Stat...