As mentioned above, all magazines, like all rifle/handgun parts, are controlled for export from the US under ITAR. If you are a Canadian, you simply cannot get the US Dept of State license to self export any of these items, regardless of cost.
Also as mentioned above, the Ruger 25 round magazines have been declared as prohibited (at that capacity) in Canada. This is because Ruger markets them for both the 10/22 rifle and the Challenger (10/22) pistol. Presumably they should be legal here in Canada if they're pinned to 10 rounds (because they're now considered to be pistol magazines) but you'd still need to get a licensed US exporter to get them out of the US. The fact that other normal capacity (i.e. more than 10 rounds) magazines exist legally here in Canada for the 10/22 rifle, doesn't enter into the logic process (if you could call it that) of the RCMP.