Jeanny, while it's been a while since I was last at Canada Place, there was no where to sit at all. It's a lot of standing around until after the security/immigration/check in process. I highly recommend flying in the day before, spending the extra money (I consider it insurance!) to stay overnight and check in later as martincath recommended. Three ships in port is a lot for Vancouver and often that causes mayhem in the terminal. I would not go early at all, not with three ships in port that day.
And I would not fly in the day of the cruise, even from Calgary. You'll probably be fine if you do, but there could be weather or mechanical issues, never mind a last minute cancellation. Hopefully, the airlines sort themselves out by July but one never knows.
I hope you enjoy your first cruise! Mine was magical!