So here's the thing, your dog is nervous of approaching other dogs on leash. This is VERY common, especially for small breeds (how is he with other dogs off leash?).
Barking is is him trying to tell other dogs "I'm not sure about you, give me space."
Walking him up to other dogs when he's being reactive teaches him that reacting the way he does is ineffective at keeping those dogs away. Therefore, it is very likely that he will try to escalate his reaction because his current reaction is insufficient.
Additionally, using a spray to startle him makes you unpredictable and dangerous in a situation where he is already stressed. At best it will teach him to hide his reaction from you, but will do nothing to change his underlying fear.
What you need to do is counter condition him, teach him that approaching other dogs is safe, that he can control the interaction, and that he has the ability to leave if he is stressed.
I'm on my phone so I can't link, but google "ahimsa BAT" for a great protocol for leash reactivity. BAT is an acronym for behavioral adjustment therapy.
Kikopup and domesticatedmanners on YouTube both have great videos that deal with reactive barking.
A big part of working with reactivity is knowing the social signals that your dog makes before he becomes reactive. There's a great little book that you might want to pick up called "on talking terms with dogs" by Turid Rugaas. Could be helpful Posted via Mobile Device