Again, it's all about the distance.
Considering you've said "surveillance, I believe he will be a distance.
I'd go for a 1dx, since you can slip 2 cf cards in, the battery is great
Then the Gps module, it is small, light weight, and won't get in the way
Both the canon iii tc's he'll need them.
A big tripod
A monopod, if he is moving
A gimball head
Bracket foots, and all the gear.
And for super length, the 600 f4 is ii
At mid. Range, 300mm 2.8 is ii
At night, the 300 will be good, because you have the fast aperature.
But there are all kinds of other possibilities based on his needs.
-modify the cameras for thermal or infared
-hook up the camera to nvg's.
At dark, there are issues
My law enforcement in Fl has a really cool system the showed me, they had...
A 1ds3 thermal image modified w/ 24-70mm 2.8
A 1ds3 infared w/ 70-200 2.8 is ii
A 1div thermal 300mm 2.8 is ii
A 1div infared 600mm f4 is
A 1div 400mm 2.8 is ii
Each system is mounted to a modified Gitzo athena head.
They have gps devices
All have the cable outlet plug batteries connected to a small power pack, and are returned to the station via satellite dish.
There are 3 capture systems and 1 spotting system.
The tech crew sets them up on ridges, in trees, anywhere.
Each system is monitored by one of the 4 tech specialists.
They've actually talked to homeland security about its possible border patrol use, butit's expensive! And only good for night.
I work as an intern for my local photography store, and they come in to upgrade and get things fixed, it's expensive, but a super expensive system.
My point is, he will be needing to see various things. When I hear surveillance, I think long range spy remote controlled cameras.
But if he just needs daytime manned shooting, it's just like a safari hunt. He brings along one body (1dx), but he will need various lenses, equipment.
And if it is something out in the desert or something, maybe even a camo suit.
The military does this stuff all the time, so try and find someone who does that.
Ask him to specify the surveillance, because there are various types he could need to do.
The setup could be simply an 800mm, a 1dx and a sandbag, but it may even be as complicated as my law enforcements.
And remember that desperate times call for desperate measures.
If he's trying to spy on teens selling drugs, a 1dx may not be necessary, but if someone is crossing the border with weapons, it could be that important.