I like to start with FamilySearch.org because it is online and FREE. They have an index to each of the US and Canada censuses. Of course, the more you know about the person you are searching, the easier it is to identify records that pertain to your individual.
For example, I went on FamilySearch.org, under menu Search > Records and entered John Ward, born 1878 in Prince Edward Island. I searched Canada records only. This entry in the 1911 census came up:
"Recensement du Canada de 1911," database, FamilySearch(https://familysearch.org/ark:/61903/1:1:27X8-QNG : 2 March 2015), John W Ward in entry for Elna Ward, 1911; citing Census, Wentworth Sub-Districts 1-15, Ontario, Canada, Library and Archives of Canada, Ottawa, Ontario; FHL microfilm 2,418,534.
I did the same search for United States records. Several records came up, but the three main entries were 1) a birth record with a John Ward from PEI as the father, but he would have been age 15, 2) a 1910 census record which specified only Canada-English as birthplace, 3) a marriage record in Michigan but again only with Canada as birthplace.
So, you see, you must start with your most recent facts and work backward through time to ensure you follow the correct person.
Good luck! -NGP