They sell wire leaders specifically made for pike fly fishing at most high quality sporting goods stores like cabelas, gander mtn, and bass pro. They come in all different strengths and lengths, but unlike the ones you'd use for bucktails or cranks, are braided and softer. That way the action of the fly isn't impaired.
You're worried about the fly sinking and you shouldn't be. Most pike and muskie flies are large bucktail flies, and in order to fish them effectively, they are often retrieved quite fast. The combination between the fast action and buoyant bucktail material causes the flies to ride high, or even on the surface. The only trouble with that is that just like with topwater plugging, you're going to get a ton of explosive strikes but they don't always connect. Still a blast and definitely a new challenge for a large predatory fish that is often quite easy to catch. Best of luck and tight lines.
