It’s the job of the Historic Sites and Monuments Board of Canada, in close collaboration with Parks Canada, to identify what is historically significant enough for federal commemoration.
Every year the board considers about fifty candidates (ninety-five per cent of which are submitted by the public) and provides advice and recommendations to the minister of the environment. National significance is a deciding factor. Uniqueness, rarity, or being first are not, in themselves, enough to make it onto the list.
Many forts and battlefields were recognized shortly after the board was formed in 1919. More recently, the board has been paying closer attention to the history of Indigenous peoples, women, and ethnocultural communities. Most nominations come from the Canadian public.
As of 2011, there are 956 National Historic Sites, 648 persons of national historic significance, and 417 events of national historic significance. Of the 956 sites, 167 are administered by Parks Canada. The rest are owned or administered by a wide range of individuals, organizations, and other levels of government.
You can find the application for national historic site designations, check the heritage status of buildings, and find frequently asked questions on their website.
Keep in mind, while you may be notified that your application meets the basic criteria within the first four months, it can take up to two years for the Minister to make the final decision.