It'll make things vastly easier for you if you take and pass the Canadian Firearms Safety Course (CFSC) and the CFSC-Restricted. Once you have your PAL with Restricted endorsement things'll go much smoother for you. You'll also have to have your AR registered and verified. You can get that done prior to importation and have your ATT waiting for you at the border crossing.
BTW: I'd simply store the 47 30 round AR mags you got, as you said you'll still be visiting the US. Keep them there and buy new mags up here in Canada. You'll find that our mag prices are a lot higher than in the US, but with the 5 round limit for "rifle" AR mags and now, the new 10 round "pistol" AR mags, you aren't going to be running cases of 5.56 through them at each range visit anyway.