My tactics to fool the guard ships of this treasures are to jump from SC and keep high speed and make a pass to scan the canisters, dodging the guard vessels. If the canisters are gold ones, i jump to SC again, take some distance and come back, but this time instead of droping on the signal i try to drop at a safer distance, lets say between 30 to 60 km away, the i approach the signal and when close enough i went Silent Running. Then i start the move towards the canisters in an angle that place me in the opposite side of the guards, (if your are lucky enough, in the previous run the sentries got away from the canisters when you meet them and follow you trying to shoot you), and get close to one canister. Try to figure out the exact place of the other canisters, so you can scoop two or three in a row. When close, (about 20mts), of the first canister, deploy cargo scoop, suck one or two canister and drop from Silent and get the hell out of there!
If you are brave enough, lure the guards away from the canisters as far as possible and restart the procedure again.
Cheers!