score:7
Unfortunately, this is a misunderstanding. Working in a hostel constitutes employment, and you cannot come to the United States as a tourist to work. Even if you're not working for money, you're still performing labor for a business and receiving compensation, which is employment.
To do this legally, the hostel would need to sponsor a visa for you (a time-consuming and expensive process if it's possible at all) and comply with federal and state labor laws, including paying wages (which is not simply "a free bed"), paying overtime, paying employment taxes and withholding your taxes, ensuring you are covered by workers compensation if you're injured at work, etc...
If you do this, you could be caught at the border and sent back. A long stay can attract suspicion, which could lead to questions about how you intend to support yourself, and they could conclude you plan to work illegally and return you to Canada. If you do wind up working at the hostel and are caught, you could be deported and banned from the US. And you'll be working for someone who has demonstrated he's willing to break the law by hiring you illegally, which does not inspire confidence you'll be treated well.