Sorry for your loss. You will have to "prepare" the tax returns separately using TurboTax and the deceased spouse's return must be mailed in. You may have to partially prepare each return in order to get the correct numbers for certain credits (such as "pension splitting"). After you have completed both returns, you can mail your spouse's return in and NetFile your's at the same time.
Here's some more information: https://turbotax.community.intuit.ca/replies/2647725