From the Toronto Port Authority website:
On May 3, between 9:00 AM to 2:15 PM, NAV CANADA will be conducting an Instrument Landing System (ILS) inspection on Runway 08/26 at Billy Bishop Toronto City Airport.
A white and blue aircraft will make repeated runway approaches, at low altitude without the landing gear down, approximately every 5 to 10 minutes.
These unusual aircraft manoeuvres are normal operations required for an Instrument Landing System inspection. Daily weather and air traffic conditions may require adjustments to the actual times of the flight inspection.