In Canada, magazine capacities are controlled, but only sort of.
Magazines are either prohibited, or uncontrolled. A semi-auto rifle magazine is prohibited if: "It will hold more than 5 rounds of ammunition for the caliber it was manufactuered." and a semi-automatic handgun magazine is prohibited if is "capable of holding more than 10 rounds of ammunition for the caliber it was manufactured."
So we import AR15 pistols with LAR 10 round magazines and use "pistol magazines" in our rifles. That is fine.
We also take 40S&W handgun magazines and put 13 rounds of 9mm into them. Also fine.
Most recently, we take .50 Beowulf magazines and put 16 or so rounds of .223 in them. Hence:
http://www.youtube.com/watch?v=Bt9a_QPFd50
Also, because I believe all threads deserve pictures: this is my Tavor with its 18.5" barrel installed next to my AR15 with its 16" barrel.