Even if you completely fooled your spouse, you were never in love with your spouse, you only used your spouse to get the PR, it's possible that you would get away with it. Somebody here told the story of a wife who was being sponsored outland not even telling her husband that she got the PR and landed. He found that out through the CIC website. He later saw her around town with another man and later she went and claimed welfare and he had to pay. The poster who told that story had sponsored his wife and she left him a month after getting PR. Even in cases like that, when the victim goes to immigration or the police, they just say, well, you convinced us it was a real relationship, now you want to tell us that it wasn't?
There was one woman on here who said she got her ex-husband deported, actually not because he left her but because when going through his PR application with a fine tooth comb, she found that he'd lied about his activities for 2 months of his life. Her being very vigilant about this as well as working for immigration probably helped.
There have also been some cases where an investigation is called. I remember one woman on here who'd broken up with her sponsor and he had immigration somehow start an investigation on her but she never came back to say what happened with that.