The Brandon Docks ctOS center is the largest of the facilities, surrounding a huge sewage treatment facility, and is one of the more secure locations.
Start at the east gate and open it to draw over the guard and then take him out with a swift melee strike. You can now enter the garage and head upstairs to take out a sniper focusing out the window, giving you a good vantage of the area below. You can use the cameras to mark the enemies and then move around to the southern gate with another guard you can take out with a melee strike. From here you can head north to a set of stairs, near an electronic sign, and take out the final two snipers with a Spec-Ops weapon.
With the snipers gone you can now use the walkways over the vats to reach the main building in the north that has the rest of the guards and access the junction box.