The nearest Rede Expressos coach station is in the centre of Porto.
The Renex Depot in Porto is situated at:
Campo Mártires Pátria 37,
Porto.
You would have to get a Metro from the Airport to Porto São Bento and then walk/cab the 400 or so metres to the above address.
For more information, see the section on buses/coaches on this page on tripadvisor:
http://www.tripadvisor.com/Travel-g189180-s301/Porto:Portugal:Arriving.And.Departing.html
Note should arrive at the Bus Station at least 30 minutes before departure to buy your ticket. Tickets cannot be bought online.
The current Rede Expressos schedule for Porto to Bragança is as follows:
PORTO BRAGANCA (227 Kms)
Depart Arrive Frequency
09:15 12:40 Daily except Sundays
12:45 16:15 Daily
14:30 18:00 Daily
16:00 19:25 Daily
17:45 20:30 Sundays
17:45 21:15 Daily
19:30 22:55 Daily
20:30 23:55 Thursday, Friday and Sunday
23:00 02:25 Fridays
