The sale of the property gave the federal Crown corporation a $109-million gain before taxes.
A year earlier, the group had a pre-tax loss of $73 million in the first quarter.
Without the property sale, company said it would have lost $58 million for the three-month period this year including a $41-million loss at the core Canada Post segment.
The company said Wednesday that it expects to report a full-year loss for 2013.
Canada Post has been grappling with a persistent drop in many forms of mail as a result of newer technologies such as electronic mail and online banking.
Besides Canada Post, the group includes the Purolator courier service and other subsidiaries.