sram,
Here it is from the Aeroplan site, my bolding:
Star Alliance Airport Lounges
As a Star Alliance Gold member, you have complimentary access to Star Alliance airport lounges worldwide displaying the Star Alliance Gold symbol. Whenever you fly any Star Alliance member airline:
Present your Air Canada Elite card and Star Alliance member airline boarding pass or confirmed ticket for a same-day departing flight to the lounge reception agent.
You can invite one complimentary guest, who must accompany you and provide an eligible boarding pass or confirmed ticket for a same-day departing flight.
Lounge access is subject to certain terms and conditions as well as space availability.
Visit each Star Alliance carrier's web site for lounge locations and guest policies.
From the UA site:
United reserves the right to restrict, alter or modify the fees, amenities, services, Club hours, locations, reciprocal lounge agreements at anytime with or without written notice to our members and customers