The 1891 Census of Canada is now available on Ancestry.ca. Although some organizations and individuals have previously extracted parts of this census, several transcripts are found online and a few have been available on Ancestry, this is the first comprehensive digitization and indexing.
According to Ancestry's press release the database, taken from 139 rolls of microfilm from Library and Archives Canada (LAC), comprises 4.5 million names and 90,000 images of historical records. From the sample I've examined the quality of the LAC microfilm copy is quite good, better than that of the 1881 census images that LAC plans on adding to their web site "shortly."
The census covers all of Canada as it existed on the 6th of April 1891. Alberta, Saskatchewan and northern British Columbia were enumerated as territories. Newfoundland was not part of Canada at the time.
Of particular interest in 1891 is information about the place of birth of the individual's mother and father.
The census revealed a situation considered disappointing to those looking to populate the Prairies following the completion of the CPR in 1885. Canada's population had grown only about 11% in ten years, compared to 24% in the US and 17% in Canada in the previous decade.
Although this is the first comprehensive digitization and indexing an interesting sidelight is that, according to "The Dominion Bureau of Statistics: A History of Canada's Central Statistics ... by David A. Worton," the 1891 census was the subject of experimental use of electronic tabulating equipment that year. I wonder what happenned to the cards!