Note that you'll be encountering a plurality of snipetroopers on this mission, so squad up accordingly. When you're ready, tag the marker surrounded by protestors.
Enjoy the cutscne, which is maybe the first time we've seen Persephone nonplussed.
The trap you need to spring is about a block away- jog over and take the lift up.
Keep ascending after the markers, until a hologram of Gaunt gives you your first official introduction to the snipetroopers.
First you'll face one, then two, then a mixed wave of helltroopers and snipetroopers. Up in the open air, the snipetroppers are more teleport-happy than usual, so if you do close with them, try to keep them pinned with specials or headshots until they go down.
When all opposition has been exsanguinated, check out the sniper's nest.
With your new intel, return to ground level and take out the truck wheel-to-wheel. You will have to fend off some enemy interceptors as you do.
When you do finally take out the van, it will catch fire but not explode. Exit your own car and search the burning vehicle.
Crash the indicated party to learn it's yet another ambush, led by a snipetrooper commander.
Her first wave of backup helltroopers will spawn in the parking garage opposite her perch, and that's actually a pretty good place to kill the less threatening enemies while staying hidden from the sniper contigent.
When you do return to the surface, use cover or cloaking to ensure you're only facing one sniper at a time. You can also climb up to even higher rooftops to get the drop on them.
When all the ambushers are down, interact with the headsets on the table.
This gives you a line on a nearby warehouse (not in the big warehouse lot). Clear out the few helltroopers outside, then open doors to reveal yet another ambush- this time swarmtroopers backed by an arc turret.
Kill all the ambushers again (why do people keep volunterring for ambush duty?), then investigate the marker inside the warehouse to complete the mission.