There is a value that is saved to the browser's local storage once you have completed the tutorial (in case you care, it's canvas-tourpoints-shown-student:"true")
I have setup my firefox to delete all cookies and saved data whenever I close the browser - so this value is also deleted.
When your canvas page loads, if this value is missing then it will show you the tutorial.
I wish the browsers would give finer-grain control over what gets deleted, but they don't. The only thing I can do is add an exception so cookies and saved data won't get deleted for the canvas site.
So, if you're getting the welcome tutorial every time you load Canvas, make sure you're browser isn't deleting the cookies and saved data for the site.
It would be nice if Canvas gave you a setting to disable it, since it will still appear when using a different computer to access the site - which, if you're in a school or university setting then I have to imagine using a different computer is the norm. This must get pretty annoying for students.