Manning has tweeted a letter from the federal government that appears to show that she has been deemed inadmissible for entry.
As per the letter she posted, she was not allowed to enter the country because of convictions similar to what would be considered treason in Canada.
The document later says that they classify her offence as "treason", which is punishable with "a maximum penalty of 14 years imprisonment".
The minister of immigration has not yet responded to Metro's request for comment.
According to the report, Manning was seeking entry at the St-Bernard-de-Lacolle, Que., border-the border one might take if they were travelling from NY to Montreal-on September 22.
Committing a crime elsewhere that would carry a maximum sentence of at least 10 years in Canada is grounds for a person to be denied entry, the document said.
Manning tweeted that she would be challenging the ban. "All applicants can expect impartial, professional treatment and clear, accountable decision-making", a spokesperson said.
At a press conference in Toronto Monday, Prime Minister Justin Trudeau was asked if he thought it was appropriate that Manning, who has been called a whistleblower, be blocked from entering Canada.
Sentenced by court martial to 35 years in prison for this massive data leak classified, she got out of prison after seven years behind bars for a sentence commuted by the former president Barack Obama.
In 2013, Manning was convicted of six counts of espionage by a military court, but she was acquitted of "aiding the enemy" - the equivalent of a treason charge in US military court.