On NaturalizationRecords.com I have links to many online naturalization records databases. Some are free, others are pay to view. It's pretty
comprehensive although if you know of a site I haven't linked to, please let me know!
AMERICAN NATURALIZATION RECORDS
|Flowers Charles USA Naturalization 1871|
CANADIAN NATURALIZATION RECORDS
I suggest doing a quick read of what is available for Canada and then choosing what fits your search time period.
UNITED KINGDOM NATURALIZATION RECORDS
|UK Naturalization Record 1865|