First of all, make sure that Tolten, Seth, and Kaim are in your party and all have Machine Killer Lv 2 or 3 rings on them -- Hacker and Lotus work. Assuming you have the right equipment, you'll need to know your opponent's offense. The Kakanas Tank will ram single characters for a few hundred damage, while the Cannon will hit everyone for a few hundred damage. The Support Tanks have weaker attacks of their own as well, but will occasionally sap your MP to charge the Kakanas Tank (left) or Kakanas Cannon (right). Now the powered up tank hit isn't too bad -- still only 500 damage or so. A Full Charge Cannon will wreck your whole damn team for 1,000 or more. Because of this it is recommended you immediately target Support Tank B.
Have Tolten, Seth, and Kaim attack it while Sarah keeps casting Zephyr. Your fifth member(Ming or Jansen are recommended) can either heal, or use Forcea. Assuming you can get the Support Tank on the right to be destroyed before the Kakanas Cannon can utilize his unbelievably powerful Full Charge Cannon, the fight will become much easier. Have someone cast Zephyra while you begin work on the left Support Tank. Once that one falls, begin work on the cannon, and then finally the actual body of the Kakanas Heavy Tank. The longer this battle goes on, the easier it becomes -- assuming you don't die that is. If at any time you do take a Full Charge Hit, immediately use Zephyra. This fight can be extremely difficult, so make sure you have all of the advantages that you can.
The Gigantes Brooch will increase your HP by a large amount, for example. Paying attention to things like this can mean the difference between success and failure. Another good tip is to remember Tolten has the ability Persistence; if he dies, and you revive him, he can not be wiped out with a single attack. This may give you the extra time you need to heal, or let an immortal get back into the fight.
Take the time to go to get Fire Proof and have this skill set for all of your immortals (and equip Blazing Fire Amulet on whatever mortal you choose). This will nullify all damage from both Full Charge Cannon and Volcannon.
Since the cannon's offensive is no longer a factor, target Support Tank A (left) first to take out any chance of Full Charge Hits. Without the cannon attacks, there will be no AOE damage, so as far as healing goes, all you have to focus on is medium-light healing from single-target tank hits. To expedite the fight, equip either Hacker Ring, Lotus Ring, or Machine Killer Lv 2 rings, and have Powerus cast on all of your melee.
Finally, after you've gotten the 2 support tanks down, target the body of the Kakanas Heavy Tank, then the cannon (following the same reason as above).