You can call Department of Homeland security and ask but they say to do DS160 and then go on appointment website and enter details and it will determine the eligibility and tell you either to do dropbox OR book counselor appointment.
Thanks for your answer, but I have read here, that we have to select few questions as Yes to eligible for Drop box.
1. Are you a resident of Canada,
2. Are you applying in the same category?
For the first one, obviously, We put yes if we are residents. Still, for 2nd one, even though we have B1/B2 or F1 visas previously issued in different countries and getting first-time H1b visa in Canada, they said to answer Yes to that question so that the system gives us DropBox Option. I even read on Reddit that people called a Consulate and got the same answer.
I appreciate your response to this if you know anything about this. Thanks