Air handlers and furnaces aren't often installed side by side in Toronto. If you rely on a furnace, you probably don't need to consider an air handler.
Air handlers are often paired with heat pumps and manage airflow throughout your house. Some units also offer secondary heating and cooling parts to support the heat pump.
A furnace runs differently by sending warm air into your vents, which send it around your residence. Since furnaces rely on combustion chambers to create hot air, they don't have some of the parts you'll spot in a normal air handler.