Here's how I'd do it.
place cursor at END of file
Match case / Minimal / Regex / Direction Up
Search for
Code:
<div class="stanza">(.+)<p>(.+)</p>
Replace with
Code:
<div class="stanza">\1\2<br />
Then repeat 'replace' as needed for each line of current stanza, then after replacing the last line, do a 'find next'