Hello, I have replied recently to this post, and since I just got my Kindle Fire 10, I found a workaround that allows me to download Canvas for Students to my Kindle Fire 10 Plus. I have Canvas on my Fire now and it works really well. If you don't mind going outside the box, How-To Geek has the perfect bypass for downloading the Google Play Store to your Kindle. The step-by-step instructions were easy enough for me to follow without making any mistakes. Here is their link: https://www.howtogeek.com/232726/how-to-install-the-google-play-store-on-your-amazon-fire-tablet/
It is important to follow their instructions completely and pay attention to detail. The whole process is pretty quick. I would read it first, then go back and do it. On the "canvas on Fire" image I attached, just long-press the links that apply to your model and open it in another tab. When you have them all downloaded, they tell you the correct order to install each one. After you have restarted your Kindle, I would let it all update about an hour before charging in to finish up. If you encounter issues with Google, it just needs time to update. You may get the occasional dialogue box on Canvas saying the Silk browser isn't compatible, but I just x it out, and it doesn't give me any trouble. Totally worth having the Canvas app on my Fire. I have used How-To Geek many times before and they are trustworthy. If you find that you did something wrong, the worst-case scenario is you have to reset your Kindle to factory settings, so make sure you back up your stuff. Now I can download my favorite Google Play apps to my Kindle Fire. Good luck!