Please don't take offence at this, but if that is what you believe, you clearly don't know much about international trade. The USA and Canada are both global trading nations whose economies depend on international commerce. There's no question of the US government not wanting you to sell your products to people in the US. It's not in their interest to stop you, nor would they have the power to do so if they wanted to.
You certainly don't need to register a US company in order to sell to Americans, nor do you necessarily need to use a US-based fulfilment house (although there might be advantages in doing so).
What you should be focusing on is creating a website where people in the USA (or any other country that you wish to target) can find out about your products, get the information they need to make a decision, and place their orders. Whether you despatch the products yourself from your base in Canada, or whether you use a third-party to do that, depends largely on the scale of the operation. If you are just starting out, I would advise you to keep the whole operation in house. As you grow, by all means consider using agents or fulfilment houses in the USA, but only when the size of your market justifies it.