set ansible-playbook user variable dynamically based on the ec2 distros

I'm creating an ansible playbook that goes through a group of AWS EC2 hosts and install some basic packages. Before the playbook can execute any tasks, the playbook needs to login to each host (2 type of distros AWS Linux or Ubuntu) with correct user: {{ userXXX }} this is the part that I'm not too sure how to pass in the correct user login, it would be either ec2-user or ubuntu.

   - name: setup package agent 
  hosts: ec2_distros_hosts


  user: "{{ ansible_user_id }}"

  roles:
    - role: package_agent_install

I was assuming ansible_user_id would work based of the reserved variable from ansible but that is not the case here. I don't want to create 2 separate playbook for different distros, is there an elegant solution to dynamically lookup user login and used as the user: ?

Here is the failed cmd with unknown user ansible-playbook -i inventory/ec2.py agent.yml