If the material is available on the online, then it is cited in the same way as any other material that is available on the online.
Template:
Author, A. A. (Year, Month, Day). Title of Material [Type of Material] (Other identifying information). Retrieved from agency website: http://...
Example:
Kamloops, British Columbia, including North Kamloops[Map] (Online MIKAN no. 3807540). (May 1914). Retrieved from the Library and Archives Canada website: http://data2.archives.ca/e/e428/e010688881-v8.jpg
If the material is not available online, then include the name of the collection, any identifying information that might help the reader locate the material, and the name and location of the repository.
Template:
Author, A. A. (Year, Month, Day). Title of material. [Type of material]. Name of collection (Other identifying information). Name and location of repository.
Example:
Milne, A.J. (1880, December, 31). Cartoon showing Western Canada up for auction. [Photo]. Archives collection. (Image No: NA-3055-13). Glenbow Museum, Calgary, Alberta.