Can you work with a trainer?
Your dog is being reactive. He may or may not actually be aggressive. The two do not go hand in hand. I work with dozens of very reactive dogs (on leash - because of the tension due to barrier) and most of them are not actually aggressive once they meet other dogs.
To fix this, it will take time and a lot of management. "Look at that" training is what has worked best for me and my students - you start the dog a good distance from the stimuli (in your case other dogs) to where they are able to function and listen to commands. When they glance in the direction of the dog, you mark and treat. You should be a distance away to where there is no reaction. Every time they look at the other dog, you mark/treat. Clickers are AWESOME to use for this type of training because the noise is a great interrupter to redirect them back to you for the reward.
When the dog is working well for you at that distance, you slowly start reducing the distance. Expect this whole process to take many months- you will need to work far away from calm dogs first, then get closer, and restart at a further distance around more excitable/reactive dogs, because they are going to egg on your dog. If you get too close and your dog starts reacting, back up a step (literally and figuratively) by adding some distance again and asking for simple attention, then marking/treating, following by touches (nose touch to hand) and sits, etc.
Having a trainer help you with this is a great idea because they can help you with your distance and timing most.
Danielle, owner of...
Fraggle Rock Collars
Fraggle Vom Richcreek CGC CA
Red Dog's Reconnaissance Man CGC
General Patton Vom Winter Storm