Integrating Marketo with multiple CRMs (Workspaces and Partitions)

We currently have Marketo integrated with Dynamics for the US. We would have Workspaces and Partitions for other regions (Europe, Asia, and more) and they have other CRM systems.

We are looking at the possibility of integrating these CRMs with Marketo via API. Is this an option? Are there any docs on how to implement the API integration? 

Any insights would be much appreciated.