Hughes told AP the woman and her husband, both in their mid- to late-20s, managed to conceal the cat from the flight crew and other passengers during the 11,300km flight from Vancouver to Auckland.
"She only revealed the cat after we insisted the bag will have to undergo further biosecurity checks.
"Apparently it was a very quiet cat. Very docile," Hughes said, adding that it may have been given some drugs to make it drowsy.
Immigration officials denied her entry into the country and instead put her and her cat on the next available flight back to Canada.
The woman claimed she had alerted officials about the cat when she bought her ticket, but MPI believe it was a "deliberate and very stupid" attempt at smuggling.
Hughes said the woman got upset about being sent back home. "She had plans to have a nice holiday with her husband in New Zealand," Hughes said. "And her cat.
"There are strict biosecurity rules in place to stop imported cats and dogs from introducing pests and diseases into New Zealand," Hughes said.
"The passenger clearly decided those rules didn't apply to her.
"This is another example of MPI and Immigration New Zealand working closely together to curtail biosecurity offences at the border."
- additonal reporting AP