This thread caught my eye, because my company has recently started an offshore contract in NE Canada and pilots were very clearly told that only Canadians need apply for slots in that contract. The company is very familiar with getting work permits for many nationalities in multiple international job sites, so I would be surprised if it balked at the mere technicalities of the Canadian work permit process
Heresay has it that the well established company in the same area has told its foreign pilots that work permits will not be renewed.
This is in an industry with a great shortage of relevant experience in Canada, ie type qualified, experienced offshore pilots, with a heavy helicopter IFR background.