This morning I found Microsoft's QnA Maker qnamaker.ai
Highly recommend it. And as the test ai is embedded in an iFrame - you can drop it straight into Canvas.
Simply prepend the iframe `#webChatControl src` with `https://qnamaker.ai` and it's good to go...
It's free and you could do some REALLY creative things with this as a student activity (i.e they make their own class revision bot)