*I am Canadian. If I want to sell online products and ship it to USA, do I need to have a corporation the USA ?
-There's no need to have a corporation in the US to sell there even if you're based in Canada. Your business is in Canada, so you should register in Canada as well. Below is a link that will help you start to register your business in Canada:
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*Is there any particularity if my dropship suppliers are in the USA ?
-Not necessarily. Large drop shippers usually require you to have a sales tax ID. You can provide them something of the equivalent form in Canada and they'll give you a different form to fill-out. Drop shipping in the US with US-based suppliers is a smart move - frees you up with sky high shipping expenses.
Hope this helps.