You didn't say what your destination was however if it is DCA, be aware that since 9/11 all passengers on the US flight from YYZ have been going through a secondary screening (can confirm that this was still occurring in August so I would assume that nothing has changed since then). This means that after clearing INS and security, you need to immediately head down to the DCA gate where you will proceed through a manual baggage examination and then be segregated from the rest of the terminal's passengers in the former RJ Canadian Immigration area. Depending on the flight load this could add an extra 15 minutes and once you are in this area there are no services other than washrooms so get your coffee beforehand.

Plan to arrive between 90 minutes and 2 hours prior to flight time for DCA and approximately 90 minutes for PIT (based on an INS line of 60 minutes - I've never flown out at that time of the AM and have found the INS lines to be much more reasonable in the afternoon and no wait for security). Luckily there is only one flight out before yours so if you time it right, the line won't be too long and at least you'll be able to sit down to wait (unfortunately, no Star lounges in T3). Also note that unlike most of the other regional flights (other than CO) departing from T3, you won't be bussed to the T3 Satellite terminal which does save a bit of time. Additionally, US has a PHL flight at 7:05 that you could be protected on in the event that you miss your earlier flight.

Edit to add some info from US' website: Check in counter opens at 4:30am. US recommends checking in 1 hour 30 minutes in advance of your flight during offpeak times (peak times at YYZ have been designated by US as Monday, Saturday and Sunday 5-8am).