How do we connect SAP Business One with Ubercart?

This can be done using SAP DI server as it is using XML based format for importing data and more suitable for external data exchange.

You can refer to below documentation for more details on SAP BI DI Server.

https://archive.sap.com/documents/docs/DOC-7699

The DI Server enables business partners to develop SOAP-based solutions to read, write, update, and remove data objects on the database level. It provides a suitable infrastructure for server-oriented partner solutions.

SAP Business One Web Services wrapper (B1WS) exposes the DI Server functionality as Web Services to provide a better usability. Developers only need to add the web references to the B1WS web services (presented through WSDL files) and use the services with the auto-generated object model. Development time is then reduced with the use of B1WS.

You can also use DI API for the same however more recommended way is via using DI server.

The Data Interface API (DI API) is part of the SAP Business One Software Development Kit (SDK). The DI API contains objects and methods that enable developers to read, write, update, and remove data objects on the database level.

With the use of DI API, users can perform the following −

Link their existing solutions "as-is" to SAP Business One, Extend the functionality of SAP Business One for missing industry-specific functionality, and Adapt the functionality of SAP Business One to fit their customers' needs. You can get more details about using SAP B1 DI API from this link https://archive.sap.com/documents/docs/DOC-7722