64bit has no SLI Support for NVIDIA
Did you name the 64bit client gw2.exe? If so, it should be working.
Desktop: 4790k@4.6ghz-1.25v, AMD 295×2, 32GB 1866CL10 RAM, 850Evo 500GB SSD
Laptop: M6600 – 2720QM, AMD HD6970M, 32GB 1600CL9 RAM, Arc100 480GB SSD
Laptop: M6600 – 2720QM, AMD HD6970M, 32GB 1600CL9 RAM, Arc100 480GB SSD