Webhook for single form, but multiple MKTO instances

Here is documentation on the developers site about webhooks:

http://developers.marketo.com/documentation/webhooks/

I am not sure I understand your use case. Could please clarify if you are trying to trigger a webhook after form submission based on certain input from the user? 

Well, technically, we will have two scenarios:

1). We have one trial form that will be used globally, however, if the user picks US or CA as their country, the lead would go into our NA instance, and if the user picks a Eurpoean country it will go to our EU instances.  If a user selects AU - this would need to send the info to our AU partners SalesForce instance.

2). We will have one trial form for mulitple products, and need the form to know which trial, based on page, to serve up to the user.

This is a great use case for workspaces and partitions: https://community.marketo.com/MarketoArticle?id=kA050000000LK8VCAW . That way, when a lead fills out your form, you can assign them to the correspodning NA or EU partition: https://community.marketo.com/MarketoArticle?id=kA050000000KyxJCAS .

Thanks Benjamin - these are concepts I did not know existed inside Marketo, however, I don't think they will help with the issue at hand.  I need to send a lead to the proper instance based on country, not keep them inside the wrong instance. From my understanding - the partition uses the same instance, just a "hidden" area within that instance.