If the parents don't trust a kiid traveling alone with a credit card, then should give the kid a prepaid (Visa) card for minor expense that must be paid with plastic, such as onboard food and entertainment purchases.

I'm not sure about Canada, but in the USA it is almost impossible to get a hotel room (a) at age 17 and/or (b) without some sort of credit or debit card with a balance or line of credit large enough to cover estimated expenses (including generous amounts for room service, laundry, phone, etc.) and damage to the room.

I'm of the "OP should not try this" opinion.