If you have a custom field (metadata) attached to a particular post, page or custom post type, you can do something like the following in your page template file:
Example example-template-file.php
<?php
$sidebar_id = 'my-custom-sidebar-id';
$my_custom_meta_value = get_post_meta(get_the_ID(), 'my_custom_meta_key', true);
if ( !empty($my_custom_meta_value) && is_active_sidebar($sidebar_id) ) {
dynamic_sidebar($sidebar_id);
}
?>
Notes: dynamic_sidebar, is_active_sidebar