In this case, the eazier way to propose all delivery method to your client is to use our frontend. More info on how to integrate it here
You can of cours create your own map etc. using our GOE6 API but it is more work and less evolutive.
When the order is created, you can retrieve labels via a simple API Call: [Create Label]. See how it work in the section C.3 Shipping Manager API of our integration manual
If you have built a plugin and want to share it with us please contact us, we will be please to communicate it in this section.