Hyeon Soo Lim's confession was reported by the state news agency KCNA.
The 60-year-old reverend of a Toronto-based church was detained in January when he travelled to North Korea for humanitarian work.
North Korea periodically detains foreigners, particularly those linked to religious activity which is banned.
Staged public confessions from prisoners have previously been held in similar cases.
The KCNA report said Mr Lim gave a press conference on Thursday in Pyongyang where he admitted to using humanitarian work as a "guise" for "subversive plots and activities in a sinister bid to build a religious state".
He also reportedly admitted to giving lectures that "North Korea should be collapsed with the love of 'God'", and helping the US and South Korea to aid North Korean defectors.
The report made no mention of how long his detention sentence would be.
Canadian newspaper The Globe and Mail said Mr Lim's church released a statement on behalf of his family, which said that his humanitarian projects were "both initiated and supported" in North Korea and "have been for the betterment of the people".
A spokesman from Canada's foreign affairs department told Reuters news agency that they are "deeply concerned", adding: "We continue to advocate for consular access and for a resolution in his case."
Mr Lim, who heads the Light Korean Presbyterian Church, had made numerous humanitarian aid missions to North Korea for nearly two decades.
During that time his missions to distribute food and clothes had expanded to a significant network of businesses, including factories, petrol stations, a fishing fleet and farms.
North Korea says a detained Canadian pastor has confessed to a "subversive plot" to overthrow the government and set up a "religious state".