Extend your Shipping Integrations to use EasyPost with an EasyPost Integration.
EasyPost has an awesome API, and they support MANY Carriers.
Additional Suggestion. Follow the "model" used by a Prestashop module I use for shipping with USPS. It uses (and requires me to use) EasyPost.
So it used BOTH API's to work, i.e. the EasyPost API and the USPS API. This enabled the developer to make a more capable and much better module than other EasyPost modules that do not do this (they only use the EasyPost API and rely on what it allows for their own feature set). So use of the carrier API's in conjunction with the EasyPost API results in much more possibilities!