I looked this up on behalf of my OH who is an NHS trainer and has been told that she qualifies for an FSW visa using this route.
If you are a Police instructor, it looks like you could qualify this way too.

http://www5.hrsdc.gc.ca/NOC/English/...spx?val65=4131

Pincher, I would not count on that.

In Canada, police instructors employed by accredited government training facilities (RCMP Academy, Ontario Police College, etc.) will have Canadian qualifications and experience, absolutely without exception.

Instructors retained by the private sector polytechnics to instruct wanna-be cops, are mostly going to be the same, except they will be recently retired members of Canadian services.

As a person with no Canadian policing experience, you MAY find a niche teaching something at a polytechnic, but it's likely to be a single special interest course and thus not a full-time gig. For example, there was a former RUC inspector teaching a course on counterterrorism as a `special interest' elective course at one of the polytechnics a couple of years ago, but most poly students in the police training stream are taking core courses that they know will make their government training (after they get hired by their agency) easier, so they will focus on getting the jump on the things they know they will have to master in the government college.

I don't know if that makes any sense whatsoever, what I just wrote. PM me if you want.

You could qualify for a visa under NOC4131 if you are a Police instructor. However, that doesn't mean to say on emigrating that you have to then get a job as an instructor. You could just join up as a normal PC on patrol, or do something else.
My OH qualifies under this as she is a trainer with the NHS teaching patient handling. There's nothing comparable to this in Canada, so she's not likely to get a similar job.
There's no rule which says you have to take up a job in the occupation that got you the visa.