Back in the days (sorry I did it in first 3/4 weeks to get that fully ship), I remember we did the cannon and void auto rifle damage. One of us had the cannon for bosses and other had the hard light and and the 3rd guy had a sniper with changing singe (borealis something). Broke the shield based on distance and when the target was staggered we used the canned to void them out and then just emptied the clip. IIRC, void did some extra damage after cannon burst but didn't matter as without the shields and with cannon stagger it was easy. Also, we found out that yellow bars near edge sometimes got pushed over the ledge when hit from up close with the cannon. Difficult to time but was helpful if it worked (saved some bullets!) Hope this helps. PS: I could be wrong as this was a long time ago and game has changed a lot since then.
Tractor Cannon lets you annihilate bosses by making them take extra damage - but you have to communicate with your fireteam to sync up your attacks and get the most use out of it.