We have a Marketo Sandbox instance and a salesforce instance as well. We want to sync both these sandboxes instance for our organization's testing and training purposes.
Could you people kindly let me know if these sandboxes sync is possible ?
We have this setup too, all you need to do is go into the Marketo Sandbox Admin settings and setup Salesforce to point to your Salesforce Sandbox, see instructions here: Setup - Marketo Docs - Product Docs. It may take a day or two to do the sync depending on your db size.