"d. These restrictions do not apply to rim-fire rifles, M-1 Garand rifles and other rare and historically valuable magazines that have been specifically exempt, plus non semi-automatic rifles (pump, lever or bolt-action)...."
CFSC Student handbook, Page 126.
It specifically references a Part 4 of "Regulations prescribing certain firearms and other weapons, components " as well as "parts of Weapons, Accessories, Cartridge Magazines, Ammunition and Projectiles as prohibited or Restricted
I would believe that modifying the magazine of a non-semi-automatic firearm in order to increase capacity would technically be legal. However, just because you can, doesn't mean you should. I don't dare think what the Conservation Officer would say if he were to inspect such a modification while you were out hunting.
It is possible, in theory anyways. It most likely requires fabricating an entire now magazine shell, as well as a follower spring. About all you'd be able to use would be the floorplate/follower. A welded/bubba'd/hackjob extension, I would imagine, would lead to all sorts of failure-to-feeds.