An individual who is a resident or deemed resident in Canada at any time in a taxation year may be subject to Canadian income tax on his taxable income (ITA 2(1)).
An individual is resident in Canada for tax purposes if Canada is the place where he, in the settled routine of his life, regularly, normally, or customarily lives.
If an individual is a resident or deemed resident of Canada for only part of the calendar year, he only has to report the worldwide income that he earned during that period of Canadian residency for Canadian tax purposes (ITA 114).
Sojourners
A sojourner is someone who is temporarily present in Canada. If a sojourner is in Canada for a total of 183 days or more in any calendar year, the individual is deemed by the Income Tax Act to have been resident in Canada for the entire year, even if he or she is technically a resident of another country at the time (ITA 250(1)(a)). As a deemed resident, he or she will have to report worldwide income for Canadian tax purposes. For those whose travels to Canada vary from year to year, it is possible to be a deemed resident one year, but not the next, depending on whether the individual meets the 183-day criterion for each particular year.
Note: Residency is not the same thing as citizenship. Citizenship refers to a national affiliation, not the place of residence. While Canada's tax system is based on residency, the tax systems in some other countries, such as the United States, are based on citizenship.
These opinions are entirely my own and do not represent any other person or organization.