As to the first part of your question, the very first part, I can confirm that you're right: in the absence of the Fair Wages and Hours of Labour Act, then a contractor bidding on a federal government contract would be obliged to meet whatever the provincial regulations happen to be, whether they're general minimum wage or specific to the construction industry.
As to the mechanics of seeking temporary foreign workers, again, I'm not an expert on that area, so I can't answer that part of your question.