As I said in a different post, once you have the Pr, you can divorce even before landing. That is why us the responsible one who sponsors have to sign a paper of immigration saying we acknowledge the commitment of sponsoring.
WHAT??? Why are you saying this stuff???
Ok, technically when you land at a port of entry you have a landing interview. It's normally not long but they do ask you if there have been changes in your relationship. If you tell the TRUTH and say yes, my sponsor and I broke up, you are no longer a member of the family class. If you lie, you are guilty of misrepresentation. If they find out, they can revoke your PR and deport you.