I found this line in the Canvas Release notes for Office365 integration and Speedgrader:
"The Office 365 LTI includes an Office 365 viewer, which can be used to preview office documents in SpeedGrader and overrides any other previewer in Canvas." (Canvas Release: Microsoft Office 365 LTI (2016-12-10) )
Is this really the case because it looks very much like Spedgrader to me. Would love to have an Office365 viewer and functionality especially as I could add comments directly to the Office document!