You do not get to decide whether to claim your marital status on your tax return. Once you are married, you must include your spouse. Once you are common-law, you must file as common-law, to be considered common-law, two people must live together in a conjugal relationship for 12 months or immediately if you have a child.
The CRA knows your true marital status based on the information you file, credits and deductions you apply for, and based on other information that is sent in which relates to you. Failing to indicate the correct marital status is tax fraud.
For more information related to this topic, please see our TurboTax blog below:
Facts Every Canadian Needs to Know About Filing Coupled Tax Returns