Can a freestanding **gas** range share 15AMP circuit with a range hood/extractor?
Steven - I am also in Vancouver, and just installed a new kitchen with permits and inspections. Yes, the gas range and hood can be on the same 15A circuit, as mine are. Just be sure that the oven is also gas, and does not have any electric broiler or electric self-clean. If the rating is under 12A you are fine. If you are splicing into an existing 15A circuit, you can install as many junction boxes as you need, so long as they are accessible by pulling out the range, or by removing the range hood's fake pipe, or by opening the door of a cabinet above the range hood. My splice is in the receptacle box that the Ikea hood fan plugs into.

I have always had gas ranges, built-in ovens and cooktops, and have never heard of CO being a problem. It should only be a problem if the flame isn't getting enough oxygen.

In the basement, you probably have a gas furnace, gas HWT and gas dryer. They all suck air. If you add a range hood and a bathroom fan, you could be seriously short of makeup air. I was required to add a 4" fresh air vent in the new basement suite. I put it behind the fridge, so that the cold incoming air would mix with the heat from the back of the fridge, avoiding cold drafts.