Ok, short and simple:

South Canal Spillway

Add more stuff in the canal itself (like in the bleedout missions that take place there). I mean the central canal, not the rest of the map. Right now it is a nice "option" to use, but I think more fighting would take place there especially in Rob/SnG and even Riot, if there were more defense positions inside the canal.

Old Sunrise City Hall

This map is quite fine, really. But I dont understand why the central building, the tower, is not accesable in the PvP game modes. Making it accessable would really improve this map in all possible PvP modes and would even a Riot on that map quite funny.

MacKenzie Sport Center

Make the swimming pool floor and roof accessable in shotout matches (like an expanding area or sth maybe).

 City Hall is my least favorite map, mainly because one base can be sniped at from the other base, and how the whole map lacks cover. Seems there is two options, run to the other base in the open and get shot from multiple angles, or take the side alley which they are already expecting. After someone plays the map a few times, the enemy and yourself becomes so predictable it becomes a bit frustrating, for everyone. I do not know if this even can be fixed, just my opinion on the map :P