There appears to be no way to paste a list into the description section when the source is plain text or Markdown.
For example, for the following newline-separated text (appears in with additional newlines in between, since Canny is a low-feature text editor):
If I use the UI to start a bullet list and then paste the above in, I end up with the first item as a bullet and the remaining items as a
list within that bullet.
If I prefix each of the original lines with any of the Markdown characters indicating a bullet list (*-+) it just pastes in as raw plain-text (does not get converted into a list).
The end result of these two things is that there is no way to have a source list that I can successfully paste into a Favro card as a properly formatted list.