Update April 18, 2015.
Nearly 2 and half years later and I would like to provide an update. The problem was discovered and solved in the Summer of 2014 when my roof/eaves were replaced. Squirrels were getting in from a small opening in the soffit where the lower and upper roofs meet. The technician should have done a better job thoroughly inspecting every inch of the roof's perimeter to find this opening.
Not very happy with mouse/rat removal services. Although the technician spent a lot of time looking for external openings, the mouse/rat poison isn't working one week later. The technician told me to call back after 5 days which I did and the answer I got from the office was that it could take 2-3 weeks and then up to two months for the poison to have any effect. I am to pay for each follow up visit since mouse removal is not guaranteed.
Also, the technician sold me the idea that a trap door was needed for squirrels where there was a small opening in the soffit. I insisted the problem was with mice/rat not squirrels. The tech refused to go into the attic and thoroughly investigate the opening from the inside and installed the trap door. Everything included, I paid $400 + HST and the problem has only gotten worse.