API = Advance Passenger Information
Air Canada says this about it:

"Air Canada (like all other airlines) is required to adhere to the Advance Passenger Information System (APIS), which requires the collection of specific information from every passenger travelling to Canada, to/from the U.S. and other countries. This information is required for the purposes of ensuring aviation safety and security.

Travellers must supply Advance Passenger Information at time of check-in or they will be unable to travel.

Following is a list of information required:

Full name (last name, first name, middle name if applicable)
Gender
Date of Birth
Nationality
Country of residence
Travel document type (normally passport)
Travel document number (expiry date and country of issue for passport)
Destination address in the U.S. (Not required for U.S. nationals, Legal Permanent Residents, or Alien Residents of the U.S. entering the U.S.) "