Views relationship between user and custom created entity
Ok ! finally found out !

I had to use the hook_views_data_alter to put the relationship on the user : 

/**
 * Implements hook_views_data_alter().
 */
function MYMODULE_views_data_alter(array &amp;$data) {
  $data['users_field_data']['cards'] = [
    'title' =&gt; t("Users cards"),
    'help' =&gt; t("Link the users to their cards"),
    'relationship' =&gt; [
      'group' =&gt; t('Cards'),
      'label' =&gt; t("User cards"),
      'base' =&gt; 'cards', // database table
      'base field' =&gt; 'owner', //database field to join on
      'relationship field' =&gt; 'uid',
      'id' =&gt; 'cards',
    ],
  ];
}