You are cherry picking one subset of supplemental farm labor. A subset that we can not fullfil ourselves. It's not to suppress wages. Immigrants who come to Canada will have 12% higher wages after one year than the Canadian median average. The farm labourers do not live here, they pay virtually no taxes, they do get affected by our high cost of living since room and board is generally provided. Admittedly that run and board isn't particularly nice. But by the same token the supplemental labor doesn't have to come work here. They do so because even though the wages are but great by our standards they are very good when they go home. I used to work side by side with these guys as a student doing the same job at them. None of the guys I worked with ever complained about the wages.

https://www150.statcan.gc.ca/n1/daily-quotidien/211206/dq211206b-eng.htm