According to this page (and the Air Canada forum lounge thread wiki), the domestic and international (which is the one LX used in the past) are open, it is the transborder (USA) lounge that is still closed. I cannot find is AC lounges are accepting *AC C/F clients like they did before however.

EDIT: Confirmed in AC forum (https://www.flyertalk.com/forum/33564514-post1362.html) that the AC International Maple Leaf lounge is available to *A partners with C/F tickets (access rules have not changed from pre-pandemic)

https://www.aircanada.com/ca/en/aco/...ounge@montreal