I'm not sure they would need to be accounted for. I think opposition to AirBNBs is a product of severe housing scarcity* and in a scenario where housing is abundant and rents are low, people would be much more welcoming of AirBNBs.
* (Or in some places like Kyoto and Venice, it's due to over-tourism complaints, but I don't think anywhere in Canada is struggling with that problem.)
Tourism is a major industry in Montreal, probably as much as venice and Kyoto with year long festivals and the fact that it is an Island is also an issue.
If opposition to AirBNB in Montreal is mainly coming from locals being upset about the excess of tourists rather than the deficiency of rental vacancies, then I stand corrected.