Get menu tail arguments of node route
To answer my own question:

So in my case the route entity.node.canonical is not defined by my own module and although I want to use it in my module with an extra parameter, I don't want to mess with it.

I have chosen to use a query parameter (using ?) instead.

http://example.com/node/{nid}?id={id}


if you need the id you can get it from the request object:

$id = \Drupal::request()-&gt;query-&gt;get('id')