ssanndy said:
can that person stay in canada and apply for pr.
or would he/she have to return to their home country for pr process?
They can apply inland and apply to extend the visit visa at the same time. They will not be deported as long as their application is in process but they shouldn't leave either because with inland, if they can't get back, they lose the application.
They can also apply outland even though they are in Canada. They would also have to apply to extend visit status if the processing takes longer than 6 months. If they applied outland and an interview is required, they would have to go back to their home country if they are called for an interview.
It is very important to prove to immigration that the relationship is real. If immigration doesn't believe that the relationship is real, they will be called for an interview. For an inland application, that can delay the processing, even for a few years. In the meantime, the person is stuck in Canada without health care and without a work permit. Inland also has no appeal rights so when applying inland, make sure the application is bulletproof. Of course better to do that for outland too for faster processing.