Send your Lander under the shore, next turn on the reef and move down using the reefs for cover. Watch out for some indirect fire if you move full range on day 4, as you won't be able to reach the next reef, however this shouldn't sink your lander. If you build a Rocket with Drake and send it to the forests under the cannons, you can complete this mission fairly quickly, however make sure to destroy units and prolong the mission a bit because your Power ranking might suffer.
As for the main navy, keep your battleships on the reefs as they're already on pretty good positions to cover the highways, use your submarines for vision (submerged) and use your APC and dock to refuel. You can also leave them overseas on some reefs.
With Kanbei start with an infantry and a mech, and start capturing and moving up. Recons and Tanks will be very helpful to get rid of the enemy's infantry/mechs and give vision, you can compliment with Artillery if you want indirect support which will be helpful if they build heavier tanks or the pre-deployed ones reach you.