No, your vent hood does not usually have to hook into your furnace. Normally, you just have a duct from the hood that lead to the outside either through the roof or a wall. In some cases and locales you may need makeup air - generally if your hood is 600 CFMs or less you won't but in some northern locales they require makeup air with less CFMs. It's makeup air that can get expensive. Makeup air is needed when there's a risk of the hood sucking all the air out of the house and backdrafting the furnace. You can search on this forum for more info on makeup air.

I'm assuming you are a fellow Canadian??? The system you are describing that your friend installed is for the make-up air. The manufacturer of the range can recommend the size of vent capacity (cfm) that is required for optimum performance, but the make-up air requirements are dictated by local building codes. My $2000 600 cfm VAH cost me over $7K to install. Your local codes should be available on-line somewhere, or you may get reliable advice from an HVAC contractor. Your appliance dealer may or may not know what is required, but mine certainly had a vested interest in "not knowing."