A peace is an interesting construct. In more quotidian speech, most of us might be more inclined to say “make peace” here. It wouldn’t take any more syllables and could be spoken with the same emphasis if necessary. But A peace is compelling in its one of many sense. There are many peaces that can be made in the world, of which this would be one and there is also The Peace, which is more broad ranging in some ways and also more local in that it is almost always used in the sense of keeping the peace or disturbing it. But Laertes is not interested in being led to a peace. That’s probably just one peace of many but the most significant one with Hamlet is his main concern.