Unfortunately, I think you will have to do 2 @ 7 days prior and the other 2 @ 4 days prior. With both flights showing C9 as you've stated above - I think you'll have no problem getting J.
If you're on AC041 to HNL, you can probably select the same seat as what you pick on the YOW-YVR flight since it's the exact same configuration in business class.
Good luck & enjoy the sun in HNL!