If this didn’t work, the person should take it to Québec small claims court aka Petites Créances, against Booking and the Montréal hotel.

The QC courts tend to have a higher standard of reasonableness favourable to the consumer when it comes to consumer contracts. “Mistakenly didn’t jack up the price for the grand prix and charged regular price instead” is not the same as “a typo causing it to offer far below reasonable cost”.

This should be illegal.