An index to the 1891 Canadian Census is available at FamilySearch Record Search. For more information on this collection, see the FamilySearch Wiki.
Images of the 1891 Census can be obtained via microfilm and online at Library and Archives Canada. See Source:Canada. 1891 Census of Canada for information on the full census.
Note that there are numerous additional sources in WeRelate for the 1891 Canadian census in various localities.