FamilySearch has added indexes to the 1851, 1861, and 1871 Canada Census to its record search site (click North America on the map, then scroll down to the list of Canadian records).
The 1881 census already was online, and plans are in place to add the 1891 census.
All are the products of a three-way partnership: Ancestry.ca provided indexes to the 1851 and 1891 censuses, and FamilySearch created indexes for the 1861, 1871, and 1881 censuses. (Both sites offer these indexes.) The originals are housed at Library and Archives Canada.
Information in these census might include your ancestor’s name, age, birthplace, religion, occupation, residence and ethnicity. Some information on the records is in French.
Note that FamilySearch has posted only the indexes, not the record images. It will eventually release record images to qualified FamilySearch members. (I believe this means volunteer indexers whove indexed a certain number of records.)
If you find ancestors in the free FamilySearch index for the 1851 census, you can use the location information to find those folks in the unindexed 1851 census images at the Canadian Genealogy Centre Web site. (The Canadian Genealogy Centre also has 1901, 1906 and 1911 census images, but you must know about where your ancestor lived to use them.)