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.
The way they've underestimated living costs and increased the ability to work for students, all while ignoring diploma-mill schools points at a pattern of knowingly allowing exploitation
Is the government allowing exploitation of Canadians by letting them work at these companies?
Canadian citizens have the same costs of living, and it's not like Tim Hortons(just an example) doesn't employee local students too.