I believe he probably did. And, if Canadian law is similar to US citizenship law, he would've found that, in order to exert his Canadian citizenship, he would've had to declare for it upon reaching his majority. Otherwise, it lapses.
Since he never did, he technically ceased to be a Canadian citizen. And, legally, it wasn't an issue.
Accordingly, it wasn't legally necessary for him to subsequently renounce his Canadian citizenship -- but he did so anyway, just to clarify matters.
By the way, I've discussed this issue with several military families, as well. The "paperwork issue" involves having to file the child's locally-generated birth certificate with the American consulate. The consulate then issues the certification of the child's American citizenship. Evidently, it's not uncommon for parents to fail to take this step at the time of birth. So that, when the child becomes an adult and seeks a passport, e.g., the paperwork process to prove citizenship with the State Department has to be gone through, say, 25 years after the fact.
Evidently, all of Cruz's paperwork was completed at the time of his birth and is on file with the American consulate in Calgary.
All of which is to say that Cruz is an American citizen-at-birth, meeting the natural-born standard, and is eligible to serve as president. Legally, his Canadian birth is a non-issue. But, politically, his opponents are trying to make it one.
Link?