Haha, Ok, I'll try and answer some of your questions.
I have no experience with the P320 Promags but the Promags I have used in the past on other platforms seem fine. No idea if there are any in Canada.
The "hi Cap" mags are the 21rd mags. Rare as hens teeth (is that still a saying?). I have only seen a few of them in Canada and never for sale. ETS makes a 21, 30 and 40rd "hi cap" mag for the P320, but again, I have not seen any in Canada.
In fact the ONLY Sig p320 mags I have seen in Canada are the OEM mags. You will have to check with your favorite Sig dealers frequently as they are currently rare as hens teeth (there's that saying again, weird) they are priced pretty high right now, like HK mags high and they go FAST.
Hope this helps.