When you are living common-law and have a child together, CRA does not give you a choice on how to file your income tax returns. You are considered to be common-law and any credits and benefits available to you or your spouse are based on your combined income.
You can prepare your tax returns separately, but you will still need to include your partner's SIN, personal and financial information. We recommend preparing the returns together and TurboTax will transfer any available credits automatically and make the best calculations for your family situation.
More information can be found in this TurboTax Tip.