Final answer:
The key factor in determining if someone is no longer a resident of Canada is if they have become a resident of another country, signaling a significant change in their life and legal circumstances.
Step-by-step explanation:
The essential factor in determining whether an individual has ceased to be a resident of Canada is B) The individual has become a resident of another country. This is because residency status is largely about where a person is considered to live and pay taxes, and if someone becomes a resident of a new country, it usually signals a shift in that person's life circumstances significant enough to alter their residency status for tax and legal purposes. Closing a savings account, giving up a driver's license, or canceling a club membership are actions that may be part of the broader process of changing residency but are not typically decisive on their own.