Thank you for your advice, and think i will now go down this road, regards mic.
If you are talking about the water show large fountain in the front of the hotel.....
If you want "over" the railing type images where they might be hugging and leaning over... be sure to take your wide angle getting up close. The water is a good distance from the rails.
The ISO is related to the camera you use, but I would think 200-400 range would be good with some fill.
If this is an important shot, why not explain to your wedding photographer that this is a image I really would like and if you could please make it happen(of course maybe you need to talk to the bride and groom if they are the ones who hired the shooter). He would be better equipt with proper flash diffuser for the shot.
Last thing you want to do on such a day is have to carry anything bulky like a extra flash.
For backup, have a Canon Gx (reduce setting for flash when close) or something handy that you can put back in your pocket, or someones purse.