I used it this past week with my Canon Rebel T3i and it fit perfectly! It was comfortable, just hanging on my right hand. I used it for a full day for an event. I also used this for my Canon EOS 7d and it fit comfortably also. Just adjust it to fit your hand :)
Are you asking if this fits in canon t3 ? If canon T3 has a standard tripod mount then it should. Product description says it should work for cannon too. "Opteka GS-2 Genuine Leather Ergonomic Stabilizing Hand Grip Strap for Canon EOS, Nikon, Sony Alpha, Olympus & Pentax Digital SLR Cameras"