Originally Posted by ffsim

That's correct, you just need an eligible AMEX card, and that's what the (unnecessarily long, duplicate-heavy) table shows. However, the "cloud 10" microsite combines two distinct groups of lounges into the heading of lounge access:

1. Air Canada Maple Leaf Lounge access for AeroplanPlus Reserve and AeroplanPlus Platinum cardmembers;
2. Canadian Platinum Lounge Benefit access for Platinum Card, Business Platinum Card and Corporate Platinum Card cardmembers.

Without reading through the T&Cs, one can misconstrue MLL access as being part of "lounge access." It is, but only if you have one of the two cards listed above in (1). If you have one of the three cards listed above in (2), you can get into the Plaza Premium lounges *without* a Priority Pass membership and by just showing the AMEX card.

In general, you can get into any Plaza Premium lounge in Canadian airports by just showing one of the cards in group (2); no Priority Pass membership required.