I am a businessperson transporting my company's inventory using my personal vehicle. I don't have a broker nor do I need one.
Anyone can transport goods into the US across a land border if under $2,500 by taking the commercial truck lane and presenting the form I linked to in post #3 to the border official in the booth and then pay any amount due for duties/taxes using a credit card. I qualified it by saying 'land border' as some airports are not equipped to deal with that CBP Form 7533. Btw, If it's above that amount there is a different procedure/form that must be used but I don't know what it is as most of my commercial goods activity is transporting goods back to Canada. The form is pretty simple and you don't even need the HTS code for the goods. Sometimes they don't even charge me anything.
Anyone can transport commercial goods back into Canada using the commercial trucking lane by presenting the other form I linked to in post #3. You can either have that form already filled out or just tell the border official in the booth what you are transporting and then be told to park and go into the office to fill out the B3 form on the computer and then any pay amount due for duties/taxes with a credit card. I don't think there is a limit to the value of the goods and if there is I certainly have not hit it even though my goods are very high value. There is a limit to how much you can charge to a credit card coming into Canada but I can't remember how much it is (a few hundred bucks). The balance has to be paid by debit card. The critical information, other than cost of goods, etc, that you need for the B3 form is the HTS code for the goods which you can look up while doing the form on the same computer and your importer number (same as your business GST number but with a different suffix - call CRA for more info).
I hope that helps.