So sorry for your loss.
If your spouse passed this year, their 2017 return must be mailed in. As per CRA, returns for those who have passed in either 2017 or 2018 cannot be transmitted via NETFILE. However, you can use TurboTax to prepare the return for print/mail.
https://www.canada.ca/en/revenue-agency/services/e-services/e-services-individuals/netfile-overview/...