Canvas and Flipgrid have an LTI integration that allows users to access Flipgrid topics from within Canvas and have points for participation be passed back to the Canvas grade book.
Please note that a new Flipgrid key and secret need to be created for each Canvas course using Flipgrid.
My suggested order of operations:
Create the Flipgrid assignment in Canvas.
Add the descriptive text to the assignment (what are they supposed to discuss)
Give it some points, add a due date,
Make it a no submission assignment and save.
Add the rubric to the assignment (otherwise, you won't have the rubric for grading)
Rinse and repeat for all of the FlipGrid assignments (topics)
Go to FlipGrid and click on your account avatar
Click on the Integrations link to get the key and secret for the course. (you need a new one for each course. It does survive a course copy)
Go to setting in the Canvas course,
Select View App Configuration,
Search for Flipgrid
Select and edit the Fipgrid configuration with the new key and secret.
Go to each Flipgrid assignment in the course and edit the assignment to change submission type from no submission to External Tool and select FlipGrid (personally I recommend checking the open in new tab checkbox)
Save the changes and then click the link in the assignment
This will launch into Flipgrid and create the topic. You can edit the topic in Flipgrid to add descriptive text or media at this point.
Rinse and repeat for each Fligrid assignment
Best Practice - The only way the Flipgrid assignment can be graded from Speedgrader is if the student's submission to Flipgrid is accessed from the assignment link in Canvas. To that end, it is best to leave FlipGrid off the left-hand navigation bar in Canvas.
I was not able to find a way to link to already create Flipgrid topics.