I frequently take AC 560 (8:35am) out of YVR on Monday mornings. At that time security is ok, but immigration is ~30 minute wait. If you're checking in at the airport, have them throw on a 'yvr fasttrack' sticker on your boarding pass just in case security has a line, but your only wait should be immigration, and probably not that bad at that early in the morning.

You won't have to deal with traffic either.