You can't. What you can do is save an image of the canvas. Is the QR Code the only thing on the page to be printed? If so, you probably will not need to build an HTML file, instead use the Custom Web View extension:
Scroll to (nearly) the bottom of that topic to find the version 12 Beta - use that version. Sunny is going to formally release it soon, it's had a good round of testing.
Custom Web View can print to available printers. How are you going to connect your Device (Smartphone) to your printer? I think you have mentioned Bluetooth - but does the printer have Bluetooth? For the Custom Web View you probably need to be able to send the image via WiFi.