1. tfws pay taxes like everybody else.
2. it is true that the taxes tfws pay don't cover expenses. that's also true of canadian citizens. virtually nobody in canada actually pays their own way and the premise that they do is one of the biggest and most malicious lies on the right. these calculations also rarely include money for things like roads. the gap is filled by corporate taxes, consumption taxes and taxes on the rich. the idea that canadian workers subsidize immigrants is false; the rich subsidize all workers in canada, and that's how it should be.
3. there's no real revenue deficit. you could bullshit numbers to generate a scapegoat, but it's general revenue. you could just as easily make the opposite argument - that tfws are subsidizing canadian workers - and it would be equally valid and equally specious and equally dubious. at the end of the day, there's no loss to recoup and no issue to address.
i would be concerned that this is step one to introduce a health premium on domestic workers.