Many here have multiple accounts and some even have multiple accounts within the same alliance (with status too).

For flights between Japan and Canada, I'd believe AC, JL and NH would be the ideal choices. I'm not too sure about JL program, so someone else might be better to explain the benefits of that program to you, but I believe AC program will benefit you more if you fly enough.

AC program will get you to *G faster, and if you make to Super Elite (or Elite IIRC), then you'll earn SSWUs for upgrades.

And finally, if you fly paid premium classes, then take a look at either BD or LH program as they award the premium passengers the most.