Ted Cruz's mother WAS a Canadian Citizen

This took a lot of research. Re: Ted Cruz citizenship

If the child’s parents are both U.S. citizens, a foreign-born child would be a U.S. citizen if at least one of the parents resided in the United States or a U.S. possession prior to the child's birth.

If one parent is not a U.S. citizen, the U.S. citizen parent must have lived in the United States for a specific period of time (until 1978, that was sometime within five years prior to the birth. After 1978, that was in the year prior to birth) ,before the child was born to transmit citizenship.

For children born on or after November 14, 1986, the U.S. citizen parent must have lived in the United States or an outlying possession for five years, of which two years had to be after the age of 14, prior to the birth of the child. 

A change in the law in 1994 enabled a U.S. citizen parent to apply for “expeditious naturalization” for a child, but it was not retroactive.

If one parent is a U.S. citizen, the U.S. citizen parent must have resided in the U.S. for 10 years, at least 5 of which were after age 14.

Some additional information may apply, here:
The divorce of Ted’s Parents must have happened sometime between 1962 and 1965 as the online Texas marriage records site (1966-2008) does not show a marriage after 1966 in Texas for these two people and under their commonly used names.

The requirements for citizenship for Ted at the time of his birth, from a birther site btw, are:

For persons born between December 24, 1952 and November 14, 1986,

a person is a U.S. citizen if all of the following are true...

..For persons born out-of-wedlock (mother) if all the following apply:

1. the mother was a U.S. citizen at the time of the personʼs birth AND

2. the mother was physically present in the United States or one of its outlying possessions for a continuous period of one year prior to the personʼs birth.

Cruz’ mother hadn’t been in the US for five years.