The Packages Service

Packages provides a Packages service which is what should be used to either load Packages or their states.

$packages = \Drupal::service('packages');

If you want to load your Package plugin with the user's settings populated, you would:

$package = $packages->getPackage('my_package_id');

To determine if your package is active which means that the user has enabled the package and has access to it (in the event that the package requires an additional permission):

$packages->getState('my_package_id')->isActive();