I spent over 40 years in HVAC as a mechanical engineer, I can tell you this..
Based on current pricing of hydro and propane (also natural gas) here in eastern Ontario, the "sweet spot" to maximize efficiency of a heat pump is when the outside temperature is between +5 and -10c. Warmer than the +5c, and the amount of electricity required to produce heat is greater than the cost of the propane required at those temperatures. Colder than -10c, and again propane is less expensive to burn to maintain room temperature in your home, than using electricity to try and extract heat from the atmosphere.
Good news is... a lot of the time between October and April, the temperature in Ontario is between +5 and -10c.
A heat pump is simply an A/C unit with a reversing valve...most of them are about 21 SEER efficiency, so savings to be had cooling in summer too.
The other big savings with a new furnace is with the blower motor...the newer and better furnaces use ECM (brushless) variable-speed motors, which can save you up to $400 a year in electricity.
The most cost effective and efficient system for an Ontario climate is a propane or natural gas hi-efficiency ECM furnace with an integrated heat pump combined with a smart thermostat to automatically switch between the two based on outside ambient temperature and current hydro rates.
If it's equipment you eventually have to replace anyway...calculate the energy savings vs the interest/investment return on the capital cost of the equipment and make a factual financial decision.