Final answer:
The Aeronautics Act is the legislation that governs all civil aviation activities in Canada and authorizes the government to enforce security measures at Canadian airports.
Step-by-step explanation:
The governs all civil aviation activity in Canada and is responsible for enforcing security measures at airports is the Aeronautics Act. The Aeronautics Act gives the Canadian government the authority to regulate all aspects of civil aviation within its borders. This includes the creation and enforcement of regulations to maintain the safety and security of passengers, crew, aircraft, and the public. While several acts such as the National Security Act and Homeland Security Act play roles in broader aspects of national security and government policy, for civil aviation in Canada specifically, it is the Aeronautics Act that is key.