He should have access:
From AirCanada.com:
Qualifying Passengers:
Business Class ticket holders
Enjoy Air Canada Maple Leaf Lounge access when you travel in Business Class and are departing on any:
■ Air Canada, Air Canada rouge, Air Canada Express flight or with any Star Alliance carrier (visit flyrouge.com for further details on Maple Leaf lounge access when you travel in Premium rouge)
Last I looked, Copa is a Star Alliance carrier and the Lounge in International is a MLL.