There's no such thing as filing "jointly" in Canada. The CRA requires that each taxpayer file a return.
If you're married or common-law, you and your spouse can choose to prepare your returns together at the same time in TurboTax. When you choose this option, TurboTax will optimize your credits between you automatically. But, even when you do this, when it comes time to file, you're still filing two returns.
You can prepare up to 20 returns in an online account. But, there's no linking or joining of the returns in your account other than the married/common-law feature I described above.