Underground Electrical run
If you could post a sketch, and some pics of the area, it would help with the discussion.
Sounds like you have a pole in the front of your house and the service entry point is in the back of the house? If your current overhead service is going to interfere with your new garage addition, the service should be moved. You can certainly do a conversion of overhead to underground and route the underground service around the new garage.
If there are any customers in the rear of your house, it may be possible to connect to a different pole in the back of your property and keep an overhead service to the back of your house.
Talk with your local utility and tell them exactly:
(1) where you plan on building your new garage.
(2) where you would like the route of your electric service.
(3) where you want to have your service entry location (if you plan on moving it).
The utility company should be able to draw/mapped out options of your service and what it will cost to install it. It could include having a pedestal/padmount on your property for the underground service.