"Obligations upon entering Canada – For information only
All air travellers, unless exempt, are required to provide evidence of prepaid accommodation that enables the person to remain in quarantine at a government-authorized accommodation (GAA) for a three-day period that begins on the day on which they enter Canada. Evidence of prepaid accommodation includes evidence that accommodation for that person has been paid for, before or when that person enters Canada. This obligation 8 does not impact boarding. Travellers are obligated to provide evidence of their booking at a GAA to a border services officer or Public Health Agency of Canada quarantine officer upon arrival in Canada.
Travellers should not be denied boarding if they have not yet booked their GAA."
Source:
https://www.atac.ca/web/images/Documents/GOC-COVID-19/Feb21/Travel to Canada 21 February 2021.pdf
Having said that, please try your best to book a quarantine hotel. There are multiple numbers now. If money isn't a problem then postpone your tickets till you get a booking. But i understand many wont be able to afford to change dates. In that case, officially no one can deny you boarding.
Someone in Australia was denied boarding and she showed this document and a couple of official tweets from the government agencies and some articles citing this. She was allowed to board. AIRLINES ARE NOT ALLOWED TO DENY YOU BOARDING FOR THIS REASON ATLEAST.