The students receive something of value (education they can't get at home) for either money directly if they have it, or cheaper labour to pay for that education and support themselves.

It's bad for Canadian workers because it suppresses wages, but it's not exploitative by default. Nobody is forcing them to come to Canada, and nobody is forcing them to work at these types of jobs. Almost all the companies employing them meet the minimum Canadian labour and pay standards.

Not that there aren't specific businesses being assholes and breaking the laws, but overall it's not exploitation.