The closed caption feature using pages in Canvas works seamlessly with a .vtt transcript.
However due to special considerations for users I'm using HTML pages to present content and provide interactivity in a short self paced tutorial. So far all of the html5 examples I've found use .js which makes them non-starters in Canvas. I have found one example but it appears to only work in FireFox:
<video id="video1" controls autoplay>
<source src="Hidden Bias.mp4" >
<track id='track1' label='English captions' src="BIAScaptions.vtt" kind='subtitles' srclang='en' default >
But it is a bit buggy in the way it displays.