Who stands to gain? Without TFWs the minimum wage (or the amount actually paid for workers) would have to rise - supply and demand.
For other things, like the aforementioned jobs at Tim Hortons, hiring temporary foreign worker is nothing but a wage suppression scheme meant to solve the "problem" of Tim Horton's being unprofitable and locations shutting down in a low unemployment environment, and the whole "temporary" thing is something to be worked around.
The previous government got in a world of shit for doing the latter and eventually stopped and banned much of the wage suppression aspect of this program. A few years back the incumbent government figured enough people aren't paying attention and re-legalised the fast food underclass again to suppress wages to address the "labour shortage" because fast food workers were faint making more than minimum wage and shudder taking a greater share of the profits of the fast food business.
Anecdotally, I've seen that fast food example often. Most of the time they think they're going to get PR in the long run.
Further, there's a lot of these fast food restaurants working employees extra hours off the table on cash