Hey Trevor,
If you got the AMEX Aeroplan Reserve card, your account should automatically update and your boarding pass will be what gets you into the lounge.
Prior to receiving my reserve card but after having been approved, my boarding pass on the Air Canada app updated to show that lounge access was included. It'll display as an extra detail in the "more info" (or similarly worded) section of the boarding pass.
This goes for all other benefits - you'll see that your ticket is reflected to be zone 2 and that your bags will automatically be given priority status.
Cheers and enjoy! Though, to be fair, I'd temper my expectations of the lounges. They are nice but nothing particularly exquisite.