According to the Raspberry Pi FAQ on Power requirements ( which can be found here --> https://www.raspberrypi.org/help/faqs/#powerReqs ):
Maximum draw from USB = 1.2A
Recommended Power Source = 2.5A
Now, according to USB specifications power output for USB works like this:
USB 1.x and 2.0 specifications provide a 5 V supply on a single wire
to power connected USB devices. A unit load is defined as 100 mA in
USB 2.0, and 150 mA in USB 3.0. And, a device may draw a maximum of 5
unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0.
Essentially, that means even if your TV provided USB3 ports that were up to spec you would not be able to deliver enough power to your Pi3.
You should check your TV's manual to see exactly how much power is being output by it's USB ports, but it is very, very unlikely it will give your Pi3 enough power. I suggest using an external power source, such as a wall jack with a good power adapter (such as the RAVPower QC 3.0 30W Dual-Port Wall Charger).
good luck and happy building!