I would listen to what they say and get there 3 hours prior. You never know what might happen to set you back. Like the previous poster said, there are many 6:30 flights which can back the lines up.
I've had a 6:30am Sunwing flight and got there at 3:30. We breezed right through check-in, and then hardly had to wait at all to get through customs and security. I would hate to arrive too much later and have to wait longer. Then once we were through customs/security, we had time to find something to eat, look in the shops and casually make our way to our gate. Flying is much less stressful when you don't have to rush through the airport.