I think the best option for you is probably AC. The fact you're moving to Canada means you'll likely be flying them a bit, so being an elite on the local airline is always nice. It is quick to get to *G (35K miles), so that'd get you lounge access, and the earn/burn ratios are much better than A3. If you think you might get to 35K, do AC, if not, make sure the booking classes you fly get 100% on A3 and that might be the best choice.
Chris