The AC website states:


Here's how to access the Maple Leaf Lounge

We welcome any customers to the Maple Leaf Lounge who are travelling in Business Class and who are travelling on Air Canada, Air Canada Rouge, an Air Canada Express flight operated by Jazz or Star Alliance.

Additional guests may accompany qualifying passengers for $15 CAD per person before 11 a.m. and for $25 CAD per person after 11 a.m. For the Frankfurt and Paris lounges, the cost is 25€ Euros at any hour. The London Heathrow Departures lounge cost is 25£ (GBP) at any hour.



Who Qualifies?

Business Class ticket holders

Air Canada Maple Leaf Club members

Altitude Super Elite 100K, Elite 75K and Elite 50K members

Altitude Elite 35K members

Star Alliance Gold members

American Express AeroplanPlus Reserve and Platinum cardholders, and AeroplanPlus Corporate Platinum cardholders

Customers travelling on a Latitude or Flex


https://www.aircanada.com/ca/en/aco/...f-lounges.html