One thing that makes Canvas too tedious to be useful is the fact that text boxes don't automatically resize as your text gorws (either as you type or when you copy and paste).
Notice how after typing a few words the text has run outside the original text box:

Here is what it should look like:

This is a really poor design choice. Even though some other mind-mapping programs have made this same poor choice, most other mind-mapping programs will automatically grow the box to fit the text and, honestly, this is the only way it makes sense.