We have access to whatever Leaf ninja we need on this, right? We should really consider all our available options.
Aburame - Sensor bloodline. (Insect scouts.) Insect control over some unknown distance. If this can be stretched far enough, could allow covert planting of stealthy explosives. Bugs are likely sacrificable.
Hyuuga - Sensor bloodline. (Byakugan.) Gentle Fist. Helps us avoid surprises within close range, lethal in direct melee.
Inazuka - Sensor bloodline. Scent & tracking. Nin-dogs. Chakra beast handling, maybe. Nin-dogs would be more obvious than Aburame insects, but might be smarter and/or longer-ranged. Would require time-delay explosives, though.
Nara - Thinker bloodline, of a different type from Keiko's. Shadow Possession. Helps optimize plans, Shadow Possession is a combat trump card.
Yamanaka - Sensor bloodline. Mindreading, possession technique. Might let us make it look like one of their own did it.
Akimichi - Multi-size technique. Soldier pills. On the whole, big & stompy; probably not a good option.
Uchiha, Uzumaki, Senju, Yasha: Sasuke and the S-rankers are too valuable to use here.
Hagoromo etc: Unknown capabilities, maybe worth looking into.
Non-Clan Ninja we know of:
Rock Lee. Nope.
Tenten. Thrown weapon and sealing(?) specialist. Might be able to make the "rods from god" or "ballista" concepts more viable.
Sakura. Known to be a good strategist, practical. I need to look up what we know of her combat skillset.
Anko. Jiraiya recommended her as reliable. Seduction/poison specialist. Not sure this is her mission.
Dr. Yakushi. Social manipulator & medic-nin. Probably knows more about Orochimaru's research than is really healthy. Probably too valuable to risk here, and unreliable besides. Also, we only suspect the manipulation half of the package.
Ebisu. Again, more useful to Konoha as a mentor than in a combat role & maybe not worth risking. Still, he's known to have a variety of exotic ninjutsu. Perhaps he'd have something helpful?
Haru. Seems to be a lightning/taijutsu user. Not really his skillset.
Kaiyo. Unknown skillset, but might be good as a political choice. May have original jutsu.
ANBU - we don't know them super well, but they ought to be the best of the best.
Our Clan
Keiko. Thinker bloodline, Pangolin summoning, Shadow Clone. Summoned Pangolin or Shadow Clones could be useful in much the same way as Aburame insects, but again, more noticeable. Can help optimize planning. Kagome stabilizer.
Noburi. Water element techniques, can sense through water or mist. Hiding In The Mist technique, chakra drain & transferral through water. Might be able to let us use the river for cover more effectively?
Mari. Infiltration & genjutsu specialist. Truth Lost In The Fog seems to be a wide-area genjutsu: despite its dangers, it might help us make this look like an accident.
Akane. Fire techniques, Kagome stabilizer. Elemental Mastery technique - boil or freeze the river? Destroy the bridge with thermal flexing? Not a huge amount of options here.
Hazou. Iron Nerve for seal recording & replay, taijutsu, decent Deception, The Hivemind. Feels kind of like we're gonna have to take him just to keep a handle on the mission, but he is the Clan Head and someone will have to be regent while he's on mission. Whichever of Noburi and Mari we don't take?
Natural Question: Does Konoha have an actual stealth expert somewhere?