score:8
Most airlines have rules about this but they are not well documented and it often varies "by mood of the day".
In my experience, the most likely scenario is: "if there is an open counter now that will stay open until your flight officially opens" they will check you in and take your luggage. In some cases they don't have to, but they still will do it.
Most likely Air Canada at YVR will accept your bags in the morning without blinking an eye, but you won't know for sure until you get there.
In many cases this is constrained by "when does the airline open the counter". I've certainly seen cases where the airline implores you to show up 3 hours before departure but only open the check in counter 2 hours before, which can be a frustrating experience. However, that's not going to be a problem with AC in YVR.