I doubt it would be acceptable or work right, but then I'm neither a pro nor up on Canadian codes. Also, lots of people think of the drain from above as a vent - it is not. Once a pipe is used as a drain, it is always a drain. To vent this group, you'd need to run a pipe up above the existing fixtures that drain into the pipe and into their vent. This is at least 42" above the floor of the highest drain or 6" above the highest fixture drain, whichever is higher. Or, you can vent it through the roof on its own.