I just imported 2 Moodle activities (anonymous survey via the Moodle "Feedback" activity) into two of my Canvas courses at https://mitt.uib.no via the same mechanism. My instructions are still valid, the only change in Canvas is that the user key is now called "Consumer key".
I advise you to paste in the xml WITHOUT any formatting characters as described. You may want to copy the screen contents of the cartridge.xml into a plain text editor (such as notepad++) first, so that you can be sure that is is pure xml. The opening tag is <cartridge_basiclti_link>, the closing tag is <cartridge_basiclti_link> and there should be NO characters (not even a white space) outside these tags.
Hope that helps.