I have Lightroom 5.6 with latest updates. It does not seem to support my new Canon M3 camera ("Preview Unavailable" when trying to upload files into Lightroom).
The Canon M3 requires Lightroom 6.0/CC2015 or later. You will need to upgrade your version of Lightroom or download the free DNG Converter and convert your Canon CR2's into a file that your older version of Lightroom can read.