You have to enroll in the beta, if you're in sandbox you should see a 'Join the canvas dashboards beta!' blue button in the upper right within the Dashboards page. Though I'll say we already have it in production and yet my sandbox says I have yet to join the beta, so that's odd. Note that you may not see Planning-related data surface in Canvas reports in sandbox, I think Planning data is still somewhat disconnected from sandbox.
If this helped you, please mark correct to help others : )