Ted Cruz's is most likely eligible to become President, but it's not 100% sure
The major fact-checkers (Factcheck.org, Politifact and the Washington Post fact-checker) have all interviewed scholars and lawyers that worked for both Republican and Democratic Presidents. Ultimately this is up to the courts, but her is what the fact-checkers concluded:
Factcheck.org:
Is Sen. Ted Cruz, who was born in Canada, eligible to be the U.S. president?
A: Most likely. The legal consensus is that Cruz qualifies because he was born to a U.S. citizen living abroad, making him a U.S. citizen at birth.
http://www.factcheck.org/2015/03/ted-cruzs-presidential-eligibility/
Politifact.com
In 2008, we reviewed research and polled several legal experts. The consensus was that someone is a "natural born" citizen if they have citizenship at birth and don’t have to go through a naturalization process to become a citizen.
http://www.politifact.com/truth-o-meter/article/2013/aug/20/ted-cruz-born-canada-eligible-run-president/
Washington Post Fact-checker:
Two of the top lawyers for the Obama and Bush administrations agree on this: Sen. Ted Cruz can become president. Legally speaking, anyway.
http://www.washingtonpost.com/blogs/the-fix/wp/2015/03/23/everything-you-need-to-know-about-the-ted-cruz-birther-movement/
