Under prevailing US law at the time of Obama’s birth, he should have assumed Daddy’s citizenship due to his mother’s age. Not the case with Cruz.
That said, it also depends on whether you are in the camp of the “old” or “new” definition of ‘Natural Born Citizen’.
Not so much old or new as Vattel or English Common Law. Both the notion of “native” in the sense of Vattel — born of citizen parents within country — and the notion of “natural born subject” — subject to the British Crown from birth — could have been the concept the Founders were adapting to the framing of the new Republic with the phrase “natural born citizen”, and precedent now plainly favors the view adapted from English Common Law.
Some of the issue is Cruz’s mom met the US Citizenship and had the time in the US required for him to qualify as a natural born US Citizen before his birth, in Canada when his parents were working there. More internet searching will bring up the Acts under which the qualifications are listed. Starting with 1 of the first acts of the Founding Congress. Naturalization Act of 1790 http://www.encyclopedia.com/doc/1G2-3407400229.html
There are other Naturalization Acts after this one with more info. It all hinged on the fact the mother had the required US Citizenship and the number of years in country to qualify her child as a US Citizen.
http://abcnews.go.com/Politics/ted-cruz-canadian-born-us-president-heres/story?id=29846887
We don’t know about 0’s mom on that issue.