We already have an unemployment problem. Letting foreigners come here and work because they feel like it will only make things worse.Then you TFWs with no controls.
That could improve the employment problem. A Canadian with skills not in demand in Canada but in the UK could easily apply to work in the UK and vice versa. I'd rather have them working abroad than sit on social assistance in Canada.
Also, foreign students in Canada support Canada's education industry, foreign workers in Canada pay taxes in Canada, and foreign businessmen in Canada can help to boost exports. Less immigration bureaucracy too.