If there are damages, airbnb has its own claims policy that can be charged to the guest so idk what ID cards are going to be useful for here. You're not doing anyone any favours here, you're running a business just like the hotel chain. Airbnb owners seriously need to get off their high horse and stop pretending like this is anything more than a transaction.
It's one thing to verify IDs in person or over video call or something. But when you're collecting sensitive, identifiable and confidential user data, you are still subject to PIPEDA in Canada. Your roof is still in Canada, so the govt rules still apply.
As a commercial entity, if you don't have a detailed data collection policy outlining why you need the data, how long you retain it and what's the data security protocol for the same; then you are in violation of Principles 7 and 8 of PIPEDA.
Even if you do have that, your request for downloadable and reproducable copies of confidential information, is in violation of Principles 4 and 5 as you're not limiting the collection and use of data. That applies when a guest is verified on Airbnb and you still ask for ID copies, because technically the platform you operate on already has said data so your collection is both redundant and unsafe.
This is the 21st century, entire billions can be stored on a drive smaller than your nails. And I don't know whether it's ignorance or arrogance, but you can't seriously expect someone to hand you their social and financial identity on a plate like that. Even if you're the most trustworthy person on earth, every app and website you use compromises the guest data that is stored and downloaded on your phone.
If a host asks me for ID copies, I just ask them for theirs before I share so I know who's liable for potential identity fraud issues. That shuts them up pretty quick because they expect guests to take risks they themselves wouldn't.