{% set category = craft.categories.group('myCategoryGroup').slug('myCategory') %}
{% set entries = craft.entries.section('myOtherChannel').relatedTo(category).order('title asc') %}

{% for entry in entries %}
    { "value": "{{ entry.id }}", "label": "{{ entry.title|raw }}" }
    {% if not loop.last %}, {% endif %}
{% endfor %}