Its not the country of origin, its the Federal approval of the ammo for sales here.
I think that has little to do with it. I'm more inclined to believe it's a business issue of WHO will be paying for the actual certification of the ammo and what profit margin the exporter would expect to earn to make it worth their while to do so.
If Wolf is unwilling to pay for the certification due to low expected sales volumes, then it would be up to individual companies to fork out the money to do so. That's not likely because for a number of reasons other than the cost of doing so.
The issue of having exclusive distribution rights to the Wolf brand would be an absolute requirement in my mind. Because once you've spent the money to get the ammo approved, anyone and their brother can then import it for sale.
If my recollection serves me correctly, it costs approximately $800 for one cartridge combination to be certified by NRCAN. That means, one bullet style/weight, powder type/charge weight, primer used, case used, and all the supporting documentation and manufacturing specifications concering that one cartridge. Change any of those variables and then it needs to be re-certified.
So, as you can imagine, if a company has multiple chamberings then it becomes a matter of economics for the entire line to become certified for sale in Canada, if approved.
There's not that many companies in Canada that have the experience or the money that could pull this kind of venture off independantly. I'd venture to guess that Marstar would be at the top of that small list.