It might, depending on the sophistication of the detector, which is illegal in Ontario, whether it is a radar detector, laser detector or a combination of both.
You run the risk of course, of being charged with possessing a “speed measuring warning device” with a fine between $100 and $1000 and forfeiture of the device.
http://archives.cbc.ca/search?q=pointts&RTy=0&RC=1&RP=1&RD=1&RA=0&th=1&x=21&y=14
Yes, it can. Convincing a court that it happened in your particular situation would not be easy.
A police officer is not likely to testify that he obtained an incorrect reading but charged you anyway. In any event the burden is on the defence to raise the reasonable doubt as to the accuracy of that reading.