I've got about 9K in credit card debt in Ontario, Canada. I moved to the US for a job, (I am a dual citizen of both countries) not to avoid paying it back. I have been unable to pay it and the debt has been picked up by a debt collector. The woman with my collection has been calling my work looking for me and has called me directly at work. She does not have my cell number and I don't have a home phone. Can you tell me if she is legally able to call me at work? If legally pursued can a summons be served to me at work? And, what course of action can she take if she is in Canada and I am in the US? Any assistance would be very much appreciated.

She may call and make any attempts to collect.

You have the right of course to tell her not to contract you further if this is a collection company, do so in writing.

They can of course always just file for a judgement against you to collect the money

If you were able to incur debt in Canada, why do you think that they would not be able to collect it? Fr_Chuck is right. You can stop them from contacting you, but you cannot stop them from trying to collect from you. If you won't communicate with them to work out a payment plan or settlement, then their only means of collecting from you becomes obtaining a judgment.