What is the difference between ADE-3410v3 and ADE-3410v2? Can I upload the firmware of ADE-3410v2 to ADE-3410v3 or upload the ADE-3410v3's firmware to ADE-3410v2?

No, there is no way to use the different firmware in the different versions. Due to production control reason, there are different hardware control codes inside those ADSL modems, so please don’t mix the driver and firmware together, otherwise this may cause the device malfunction.
Thus, the ADE-3410v3's firmware and driver only can be used in the correspondent models.