For the people worrying about the five- versus six-shell capacity in the cylinder, or whether the cylinder is a magazine: it doesn't matter because this is a double-action firearm, not semi-automatic, so magazine capacity is not regulated.
Go to
http://laws-lois.justice.gc.ca/eng/regulations/sor-98-462/fulltext.html and Ctrl+F for "semi-automatic" and you will find:
"In these Regulations, “semi-automatic”, in respect of a firearm, means a firearm that is equipped with a mechanism that, following the discharge of a cartridge, automatically operates to complete any part of the reloading cycle necessary to prepare for the discharge of the next cartridge."
The preceding definition does not apply to a double-action mechanism, as nothing happens automatically after the cartridge is discharged.
Legal Beagle stuff aside, it looks like it's mounted to the 6-o'clock rail, but adjusted to be in contact with the front of the magwell to put the recoil stress directly on the lower receiver, rather than risk shearing the takedown pins or stretching out the takedown pin holes like the MasterKey does.