When you are moving any kind of cargo across an international border there is always a certain degree of paperwork which must be completed beforehand. The extent of this paperwork depends on a great many different factors, including what the item or items are that you're shipping, the value of the items, if there are any extra treaties or laws governing the importing and exporting of those items, and where the items originally come from.
If you have any confusion about what kind of documentation you need to or should include with any of your shipments that are going from Toronto into the United States, then you should first discuss this with your Toronto delivery company. They will likely be able to point out to you all of the documents you need to have filled out in order to have a smooth shipment of your cargo into the US. It is also in their best interests to ensure the process goes smoothly because in most situations they will have more deliveries than just your on board their vehicle, and a delay from one order will delay them all, something that will not make the company itself look very good to its customers.
The single most common piece of paper that needs to be included when making a cross border shipment is a commercial invoice. The only items that escape this are tiny gift items of nearly no value, and it is simply safest to include it in anything you are shipping across the border, simply to avoid confusion later on. Any Toronto delivery company that has experience in moving goods across international borders will likely also advise you that a B13A export declaration form might be necessary if you are shipping cargo or freight in any volume to the United States. If they can't provide one of these forms directly to you to fill out they will point you to where you can print one off of the internet to fill out before your shipment is picked up.
If certain other preconditions affect your shipment there may be other forms you need to fill out. Goods that are covered under NAFTA have separate documentation that needs to be completed, as do goods of extremely high value. Simply talk to your courier about this and they should be able to tell you the exact forms that you need to fill out well in advance of the pickup date for your delivery.