It's true that from Canada to Asia, SkyTeam options are limited, and within Canada, of course AC is your only alliance-airline choice.

On the other hand, traveling from YUL to Europe or the Middle East, Star and SkyTeam are pretty much equivalent. (I just took KL's AMS-(DMM)-DOH flight last week, which is a fine option.)

I currently have Elite Plus with SkyTeam (NW) and Gold with Star Alliance (UA), with travel patterns quite similar to yours: business trips mostly to the Middle East (usually in paid C), lots of flying within North America O/D'ing from *A hubs (in the U.S., mostly involving IAD, SFO, and LAX in my case), and a few trips to Europe (usually paid Y) and Asia (usually redeemed F) each year. I find that *A suits me better, as I can rack up redeemable miles and status via domestic flying, I fly most of my international trips from IAD or SFO, and I can use United SWUs for upgrades on trans-Atlantic segments.

If you are considering *A, you might look at United Mileage Plus. I don't know in-depth how it compares to LH or AC's program, but in terms of earning redeemable miles and SWUs, it might be preferable to LH for a North America-based traveler. Of course SWUs are only available if you are 1K status (100,000 EQM), which would mean that you would have to fly almost exclusively on *A.

If you are doing a lot of trips within Canada, that puts you on AC. So, I suppose the question is whether you want to concentrate all of your travel on *A or perhaps try to achieve the equivalent of *G on both *A and SkyTeam, which might be an option.