we have a custom CRM setup

When a Deal is created the derived Tasks' owner is the creator of the Deal. However, I want it to be the Marketing Coordinator of the unit. Every unit, which is a required field of the Deal, has a chosen user as the Marketing Coordinator. I want to have the owner switched and the new one notified when the Deal is created or unit field is changed. 

I tried creating a workflow where I can successfully assign the Units owner to be the Deal owner but I don't see a way to get Marketing Coordinator from the Unit.

is there a way to do this using assignment rules?

should I be using blueprint instead of workflow?

should I be using a custom function?

could someone help me find a solution

thanks