Any Magazine designed to fit the M&P15-22 has to be pinned to 10rds as there is a pistol version of the rifle. This is the RCMP site for mag restrictions
http://www.rcmp-grc.gc.ca/cfp-pcaf/bulletins/bus-ent/20110323-72-eng.htm Item #1 states this plainly. Black dog drum mags don't require pinning as they are designed for other rifles (10/22 or .22 ar-15 Conversions) and you modify the drum tower to fit the 15-22. This is perfectly fine based on #4... Ie drum is made for a 10/22 but after modification can fit a 15-22, as it's made and intended for the 10/22 it doesnt have to be pinned. I've found other mags that with modification will fit the 15-22, since these mags weren't designed for the 15-22 but for another rifle (and they still will fit the other rifles) there is no requirement to pin them.
That being said... If a police officer believes that your mags need to be pinned and wants to confiscate them (or more), you probably will have a hard time explaining that they are legal and may take a long time and a court date. Most police understand Canada's convoluted gun laws as well as most people, which is that they could easily get confused.