That's not an easy answer. And anyone who answers it would only be guessing.
General belief on this forum is that FP is sent when your full or partial name, and biographical profile results in a hit during RCMP's criminality and background check. They need your fingerprints to make sure it's not you.
There are tons of posts/threads on RQs.
@dpenabill covered it extensively. TL;DR version: it could be randomly sent for quality assurance, or it could be sent when the officer reviewing your file suspects your claim of days on which you were physically present in Canada (I would think this could happen if the dates on the physical presence calculator are incorrect or if you failed to account several/long trips outside Canada). Also, sometimes a short version of the RQ is given during the interview, from what I've read on the forum, for the same reasons.