You could attempt Hyper Metal Sonic's voice from the original film, but if you do this you should add some emotion into his words. Alternatively you could try making him sound a little like Sonic. Other than that, feel free to give him a voice you think he would have. 

Movie bio: Shard is the rebuilt Hyper Metal Sonic, having been rebuilt by Tails when Knuckles discovered his jewel shard still intact at the North Glacier. He shares a lot of Sonic's attitude and personality, though he is quite insecure about himself. Shard is loyal to his friends and sees Sonic as his brother, and he also sees some form of goodness in the new Metal Sonic which Eggman has built.