IIRC, CIBC has a contract to supply ATM's all over Pearson airport, so I'm guessing it is unlikely you will find another bank's machines at any of the terminals. However, according to HSBC's website, it appears that an affiliated machine from the Airline Financial Credit Union is located inside the Viscount Road parking garage (6145 Viscount Road Room 413) which is a short train ride away from the Terminal 3 towards Viscount station. Once you get off the train at Viscount, follow the crowds going across the bridge to the parking garage, and the credit union is on the right side.