I want to use my own portal to establish Fabric VCs

Yes, Equinix Fabric has a robust set of APIs. I'll post a few helpful links below:

The Equinix Fabric APIs are a collection of RESTful APIs that allow you to programmatically create, order, monitor and delete private virtual ports that connect to Equinix Fabric. (Refer API reference section or Catalog for more details.)

https://developer.equinix.com/

• How-To Guide - v4 APIs
• AWS Connection
• Azure Connection
• GCP Connection
• Oracle Connection
• IBM Connection
  
  Video links (using V3 APIs - but it is still valid and is good for understanding purposes)
  
  AWS - https://youtu.be/UEM2-QOpQAU
  Azure - https://youtu.be/M2vAdF9NuWI
  GCP - https://youtu.be/VZKPDqqHscw
  Oracle - https://youtu.be/lVa3NpLepiM
  IBM - https://youtu.be/Mg1TwWfE8qY