Originally Posted by KVS
It will be at the discretion of the lounge agent in question. So the more proof you have of your *G status, the better. While a print-out of an online statement will work in many cases, you can increase your chances if you get a faxed letter from Aeroplan confirming your *G status.
However, keep in mind that technically, they can deny you access if you don't present a valid *G card when entering the lounge.
I never had problem when I lost my card and printed out the statement and had a fax from AC, only Singapore hassled me and they still let me in.