As a PR, you have the right to live in any province you want to. Most PNP's make you sign something stating that you intend to settle in that province but intentions may not always work out. If you get a job somewhere else, nobody will hold it against you if you move.
what if immigrant got job offer in Ontario while Quebec skilled worker application was in progress, after landing & searching for job in Quebec, he decided to take the Ontario job offer offered him long time ago, is this legal, if so, how so?
It is legal because there is no law against it. A PR has freedom of movement in Canada. That means you can settle and work in any province.
No PNP makes you sign an absolute contract to remain in that province for a certain length of time. They only make you sign a document stating that you intend to settle in that province.
As long as you intend to settle in the province when you sign that statement and later when you land as a PR, you are not lying about anything. If it so happens that you can not find a job in that province and you find a job somewhere else, it is only natural to assume that your intentions will change.
