Do not kill any guards
Sabotage cannon: 0/2
Haytham needs to escape from the fort now. If you went and sabotaged the cannons then you have a very easy, if long, out. Head back to the second cannon, hop the wall and go to the edge of the ledge. Make a leap of faith from there into the river below. Swim on over to Kaniehti:io and talk with her to finish this mission.
Otherwise you can just make a quick run for the front gate and have to lose the guards in the wilderness before you can finish the mission. That takes some time.