The future of an entire city block in Vancouver's downtown core is now up in the air, after Canada Post finally let go of its signature mail processing plant.

The Canada Post building at Georgia and Hamilton street has been sold for an undisclosed sum to the British Columbia Investment Management Corporation (bcIMC), a pension fund management company.

Donald Luxton, president of the Heritage Vancouver Society, said his group will be closely watching the progress of any changes proposed for the site.

"It's building that we consider to have significant heritage value, which is not officially recognized in any form of protection or even heritage register listing of the building," he said.

"We feel it's a very significant piece of mid-century architecture, and public and institutional civic architecture," he said.

Luxton said Heritage Vancouver would like the city to assess the building for heritage value before anything drastic is done.

"Our position is that the building would have significant heritage value if it was evaluated, and we think alarm bells should be going off on this issue," he said

The modernist building, which opened in 1958, does not have an official heritage designation, which means it could be demolished.

But Vancouver City Councillor Geoff Meggs says nothing would be done to the redevelop the property without input from various parties.

"There's no requirement to keep the building exactly as-is, but changes would have to go through some kind of approval process and there would be assessments of the heritage value, and recommendations coming from professionals about what can be protected and what could be changed," he said.

Georgia and Hamilton, Vancouver, B.C.

In 2011, after Canada Post announced the relocation, Meggs suggested the building could serve as a new, larger home for the Vancouver Art Gallery. The city had already reserved a site for a new gallery two blocks east of the post office at the corner of Cambie and West Georgia streets.

In a statement, the bcIMC says the building provides a unique opportunity for a large-scale mixed-use development, but says a redevelopment on the scale of the existing full-block building would require extensive planning.

In 2014, Canada Post will begin shifting the operations into the new 700,000-square-foot processing facility being built at Vancouver International Airport in Richmond, B.C.

With files from the CBC's Robert Zimmerman