Air handlers and heat exchangers aren't often installed side by side in Toronto. If you rely on a heat exchanger, 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 heat exchanger runs differently by sending warm air into your vents, which send it around your residence. Since heat exchangers rely on combustion chambers to create hot air, they don't have some of the parts you'll spot in a normal air handler.