Hey Tuyet!
I've been putting a lot of work and google into this the past week or so. As near as I can figure, you must get a ITIN (Individual Tax Identification Number) from the IRS to qualify for the tax treaty exemption. It does no good to fill out the information on the AirBnb website form without that number, but (I am assuming from what scraps of information I could find online) once you give AirBnb that number they stop withholding US taxes.
Okay, here's come the tough part. To fill out the W7 form and get a ITIN, you have to submit proof of your citizenship to the IRS. They will only accept original documents (which means mailing my passport to them and waiting for it to be returned in two months) or "certified copies." I'm not parting with my passport, so the question is, what's a certified copy, and how can I get one? Took a fair bit of googling to find the answer.
There's two options. One is to go to the Canadian passport office and for a small fee of (I think) 45 bucks they will give you two or more photocopies that are "certified" by the Canadian government. I'm in LA, so I can't do that.
The other is to go to an "Acceptance Agent" in the USA who is an accountant that has been vetted and approved by the IRS. They will photocopy and verify the passport, and you can mail the certified copy in. The first and only acceptance agent I've gone to thus far wanted to charge $350 bucks to do that, so I'm hunting for another that might be cheaper.
The third option, actually, is to book an appointment in person with the IRS so they can verify my passport in person, but because it is tax season, they're all booked up for the next two months.
So, I'm currently on the hunt for an "Acceptance Agent" who will certify my passport copies for cheaper. Maybe even free? One can dream...
For you, my understanding is the best thing to do would be to go to the passport office in Vancouver. Pay for the certified copies. (Get as many as you can, I'm told there's no extra fee for more copies.)
Then either get a US accountant to help you or do it yourself: fill out form W7 and submit it with the copies and a tax return saying you earned zero dollar in the US. You'll get assigned an ITIN in about six weeks. If AirBnb has been withholding taxes, my expectation is that the IRS will reimburse you. You can then add your ITIN into the form on the AirBnb site to avoid getting taxes withheld going forward, until the ITIN needs to be renewed. I think every three years, but I may have misread that, I'm not sure.
The whole process is super confusing and unclear! 🙂 I've tried to make this reply as clear as I can. I hope it helps.
Good luck, I'll try to update here when (if?) I get it all figured out.
CAVEAT: I am not an accountant and anyone should follow any advice or suggestions I have made under their own risk!
ALSO: If anyone can correct me or help me where I've gone wrong, I'd REALLY appreciate it! And so would a lot of other people, it seems.