Hi,
At this moment I guess that HikaMarket can help you for your task.
You can configure HikaMarket to set the managers as vendors. At this moment, each order made can be assigned to a specific manager who will be noticed by email.
In HikaMarket there is a "vendor selector" feature. It allow you to create an order custom field (HikaShop business required) and assign the entire order to a specific vendor that the customer can choose itself.
I don't know afterwards what you want the manager will be able to do but in HikaMarket, the vendors are limited for the order edition. They can change the order status but not much more.
The main vendor can access to every order elements and modify them like he wants, in the same way than in the HikaShop backend.
So, depending if you want to let more specific rights to your managers, a mix between specific vendor and main vendor can be required.
But at this moment, I will require more details about what your requirements.
Regards,