I lived in Canada for over 20 years, just came to HK 2 years ago and i'm holding a HK HSBC EPS card here. Was also using a HSBC card when I was in Canada.
I doubt you can use a HK HSBC card in other countries. HSBC is worldwide but it doesn't necessarily mean all accounts (provided you have an account in different countries) sync. My money in Canada is ONLY my money in Canada and vice versa.
Yes you can use your card in teller machines overseas (not necessarily HSBC ones) providing it has the "plus" logo (or an equivalent). Although you cannot withdraw at HSBC counters overseas with your card the same way you would in HK.