回复：H1B第三国(加拿大)签证,面试时该说什么理由?

They seldom asked this kind of question.You can tell them that you need to go back and forth between USA and Canada (for visiting relatives). Immigration officers suggest those whe cross the broder a lot apply for a visa.
By the way, I got a visa in Toronto a few years ago, and the policies have been changed a lot. You are suggested to confirm with somebody that you can apply for a H1 visa in Canada (if you are not a perminent resident of Canada).