Police confirmed that the pair, a Greek couple, are expected to appear at Edinburgh Sheriff Court on Thursday, June 17.
They were arrested earlier this week at separate locations in the Capital - Granton Road and King George IV Bridge - over the incident which sparked a major police response in the city centre.
The suspicious item was discovered in a public shelter in the gardens on January 11, 2018.
Army bomb disposal experts were called in and a controlled explosion was carried out about three hours after the alarm was raised. No one was hurt during the incident.
Detective Chief Superintendent Stuart Houston, Police Scotland’s head of Organised Crime and Counter Terrorism, said officers from Scotland’s Counter Terrorism Unit carried out enquiries following the discovery of the item, including with European partners and law enforcement agencies.
He described it as a “protracted and challenging inquiry” to identify those believed to be responsible.