I have never tried to make it a checkbox list, but you could just try something like the following:
@EVAL $output = $modx->runSnippet('getResources',array('parents'=>'0','tpl'=>'@INLINE [[+pagetitle]]([[+id]])==[[+id]]','outputSeparator'=>'||','sortby'=>'pagetitle','sortdir'=>'ASC','limit'=>'0','showUnpublished'=>'1','showHidden'=>'1','depth'=>'3')); return $output;
insert this into the "input options" field of your tv (doesn't matter if checkbox or multiselect list).
We had a rich discussion about that here:
https://forums.modx.com/thread/?thread=79645&page=1
maybe you find some more info there (and if you find a way to make it work with wayfinder, I would be very interested =D)
