That statement gives you away. You say you do not believe that anyone can reasonably assert that Cruz owes any allegiance to Canada. The eligibility clause does not say that each candidate must be tested to find out if it can be reasonably asserted that they owe any allegiance to another nation. The Constitution was written to exclude a group of citizens that might have any possibility of a divided allegiance. We do not even get to test Ted Cruz because he is already not eligible.
Once upon a time, conservatives believed in the doctrine of original intent, in which judges interpreted the Constitution based upon the intention of the founders - not the expediency of a short term politicialy motivated desire by a buffoonish faux conservative candidate to vanquish his leading challenger from the race.