Yes, the Audi A3 diesel would be a suitable car for long distance drive. The car is comfortable as well as the 2.0 litre engine is well refined. Do remember to take certain pauses during the journey to avoid access heating of the mechanics of the car.
For this, we would suggest you walk into the nearest authorized service centre as they will be the better people to assist you. You can click on the following link to see the details of the nearest service centre and selecting your city accordingly - Service centre