a) Go north. The mission is too important to risk being discovered and, even Martel admits, there is a natural crossing there. You will be able to cross and won't be discovered thay way.
b) Go south. The ferry can carry horses across and there is little risk of falling to your death. It'll take time for the Steward and the Black Blades to mobilise even if you are discovered.
c) Rebuild the bridge. The canyon isn't that wide, and there will be more Rangers needing to cross this way. It will at least speed their journey.
So? Which is it, Sky Road walker? Vote! Share! Good luck!