Is it illegal to promote someone in Canada for sleeping with the boss?

Recently a coworker of mine got promoted for a job they were not fully qualified for, and there were several other candidates who were either just as qualified, if not more qualified for the position. The coworker who got promoted is currently in a sexual relationship with one of the managers and was promoted in a hasty manner. Our policies state that you must be competent in your role for more than 6 months, but this coworker has not been doing their job coherently for the last 3 or so months, in fact, some of the management was discussing how she couldn't manage to understand simple tasks and procedures correctly within the last 2 months.