I didn't try entering the lounge without the card, since I entered as a guest on my husband's AC Elite status. (But I was told previously that they would require seeing the card).

That said, my Air Canada boarding pass did show me as Star Gold (printed as A3 *G) and I was able to pre-board on AC using that alone. I'm sure there's a good chance that I might have been able to get into the lounge by showing that if I b*tched enough.