My understanding was the discussion is about undergraduate study ("second-year chemical engineering student").
International students in Canada can get work permits without much difficulty, and have a relatively easy path towards permanent residency & naturalization once they graduate.
The reason so many international students enroll in graduate studies have nothing to do with how much they can get paid flipping burgers, and everything to do with why they are enrolling in a foreign program in the first place. A graduate degree significantly improves their career prospects at home, and opens a lot of immigration doors abroad.
Some universities are addicted to foreign student money and could not survive long without it (not even the tuition premium: just having 40% of students from abroad).
Some others are pretty much living off endowments. They could shut down international admissions and give full rides to everyone and still make profits.