If your assignments are using the Turnitin "one-click" option -

After January 7, 2019, this "one-click" option will not be available and your assignments will not have Turnitin enabled for your assignments.  After this date, there will be two options available within Canvas for your Turnitin needs.

Turnitin can be used two ways within Canvas: the plagiarism review option and the external tool. Turnitin is also accessible through their website.

The plagiarism review is great if you want to use all the native Canvas assignment features such as the Canvas rubric, differentiated due dates, peer review, group assignments, allow multiple submissions, or use the SpeedGrader for student feedback.  The external tool is the integration to use if you want to use the Turnitin rubrics, PeerMark, or want to provide student feedback using Feedback Studio and GradeMark.