Go visit Landon again in his usual haunt and you’ll find yourself heading towards the town of 'Escalera' to save some prisoners from execution. Once you reach the convoy of carriages holding the prisoners, you should ignore Landon’s idea and instead attack from the rear first.
Shoot the guards surrounding the carriages first, then speed up and auto-aim lock onto the driver of the carriage closest to you. Kill him with your rifle and Landon will jump into the driver’s seat. Speed on up and gallop towards the carriage up ahead.
Again, shoot the driver of it to stop it, jump on board and drive it towards the newly completed bridge that’s joined with America. When you get closer to the bridge, get your trusty rifle at the ready and shoot all the guards surrounding the bridge.
There’s some TNT crates nearby, so make these your first target, before mopping up anyone left. Take it slow across the bridge and use your rifle to pick off anyone still trying to fire at you. If you like, you can also simply speed across the bridge and if you make it to the yellow cross, you’ll automatically finish the mission safely.