My dad's gen 4 (LE I4) came from the factory with heated mirrors, which I didn't know until I took apart one door and try to figure out the wiring to put that in. Go figure.
Seriously I'd think that the said heated power mirror will have two additional wires and a different plug. The extra wires would need to be wired to your defroster switch, so the element heats up with your defroster.
Download the manual from camrymanuals.com and the wiring diagram will tell you how to hook it up. Good luck. Junkyard is your friend.