No, it's not an open market. The permanent resident program simply requires them to have two years of work experience in a relevant occupation. It doesn't matter whether it's with one, two, or three employers.
The work permit under which they come to Canada is normally for a specific employer. However, they can switch employers if they are offered alternate employment.
We're hoping that outside of the live-in environment they will feel more free to respond to improper treatment by an employer, whether it be unpaid overtime or other types of unfortunate situations.