What are the requirements to obtain the ATP license in Canada?
The requirements for ATP Aeroplane are in CAR 421.34. You can read the details yourself, but in summary:

Be at least 21 years old
Hold a Category 1 medical
Pass 3 written exams
Hold a Commercial Pilot Licence - Aeroplane (valid for both day and night flight)
Have 1500hrs total time, of which at least 900 must be in aeroplanes (see the regulation for more details on night, XC and instrument time)
Within the last 12 months, demonstrate instrument flight and emergency procedures in a multi-engined aeroplane