From the RCMP Site:
http://www.rcmp-grc.gc.ca/cfp-pcaf/b...323-72-eng.htm
1. Magazines designed or manufactured for both rimfire calibre rifles and handguns
Magazines designed to contain rimfire cartridges and designed or manufactured for use in a rifle do not have a regulated capacity. However, magazines designed to contain rimfire cartridges and designed or manufactured for use in a semiautomatic handgun are limited to 10 cartridges. Magazines designed or manufactured for use in both rifles and semiautomatic handguns are subject to the handgun limit of 10 cartridges.
Example:
Smith & Wesson M&P 15-22 rifle and 15-22P pistol chambered for 22LR caliber:
the 10 round magazine is unregulated
the 25 round magazine is a prohibited device
Example 2*: The Ruger BX-25 magazine, chambered for 22 LR calibre, is designed and manufactured for use in the Ruger SR22 rifle, the 10/22 family of rifles/carbines and the 22 Charger handgun. As a result,
this magazine is a prohibited device unless modified so its capacity is 10 cartridges or less. (*This information was not included in the original version of this bulletin, but was added on 2013-09-05.)