As a Canadian PR, one is free to stay anywhere within Canada.
But since they ask us to fill schedule 4, which states and I quote, " I declare that my family members and I intend to live in the Province that nominated me", means that we are bound by this in a way. Now, what they would do if you decide to break this bond, I cannot answer.
But out of courtesy, I would personally stay in the province that nominated me. I was very clear on the province I wanted to stay and luckily for me, they invited me.