Max Payne 3

I did this with a group in Gang Wars on the Panama Canal map

The hardest part was identifying where the observation deck is.

To find it, note where the visitor's center is from the single player campaign. The observation deck is to the left (facing the visitor's center) and is a 2 story small building with lots of windows. You need to climb up in the building and aim through the windows at the yacht and shoot / kill someone on the deck of the yacht

Ed E Nigma's guide for finding the observation deck works very well. Just make sure you are in the little building in the back right corner of the map (if you are facing the yacht) and kill someone on the deck. A sniper rifle makes this much, much easier. If you can have your buddies defend you in the building, that also helps! There is a spawn point on the deck of the ship, so if you are patient, and stay alive, you should eventually be able to snipe someone.

The Canal de Panama map is listed as "Mobsters on Vacation" in the Gang Wars mode. I think it can also show up as "International Intervention." It is sometimes called "Pacific Approach" in Deathmatch/Team DM.

I had a little trouble figuring out what the map was called in Gang Wars, so I thought I'd share it here to help others avoid the trouble.