Well , There are few classics car transport companies based in Canada(I couldn't find any in Us) that do the broker service. They are Licensed and bonded as broker . Almost all classic car dealers in Cananda have a working relationship with such truck companies .... you should be able to look them up, or call any classic car dealers in Canada and they should be able to help you.
From my calculation for a one time customer the trucking company will charge in neighborhoods of 600 to 700 for brokerage fee. This is based on dedacting my estimate of shipping charge (based on distance) and couple of quote I received back last year when I was contempling buying a nice looking 73csi last year in Calgary which didn't work out ..
You best option (least costly) If your friend buy it for you and bring it across then you can buy it from him.
Please have in mind the broker will fill out a lot more paperwork than an individual. So you still have to fill out some of this paperwork perhaps more any ways .....so using a broker, I guess, have more paperwork for (not sure)
Few more points / reminders:
You should have a sales agreement or some sort , or intent to buy between you and the seller ( or your friend and the seller) before you send anyone that way. Have a copy with you when you cross the border. Perhaps even copy of the ad and how you found the car. This will help you show your intent for entering to Canada with plenty of cash in your pocket...
2- if you carry cash across the border declare it on BOTH SIDE... A) on the Amercian side first and B) immediately after , with Canadian authorities. They are next to each other. Also call the US Custome and border control for that location and let them know what your plan is. That will help you or friend get a feel easier about it.
3- you will be required to pay 2.5 percent of buying price as tarrif upon arrival at the border. However you handel the bill of sale it's up to you... so a bill of is what is used to calculate your buying price for authorities at the US customs. You pay in right there. They will stamp the paperwork you filled out and you leave with car either on trailer or drive it across.
4- transfer of title is different in Canada. You don't get neither the Title nor the TAG ( you will be tagless upon arrival into us ... may be your friend wants to take his trailer with him(best option I say) . So only one person is required to go and pick it up too. If you decide to drive into US each state bordering Canada can sell you "three day temporary tag"for like $30. I had to buy one in washington state and spent two hour finding out where to buy it (drugstore in my case) and drive 25 miles to get there . I asked the dealership to evaluate the car for long trip . I drove the my car from ChiliWack to Seattle and left it at BMw dealership waiting pick up by transport company for three week. I prearranged that for service in advance with a particular date .They charged me $130 for inspecting the car and list of items it needs , and telling me the car is not road worthy and I asked to keep it there for three weeks. That was really the main reason I did that as I already knew the car had been sitting for 10 years and even though the seller has brought it back to life it still had plenty work to do.
All and all it is really easy once you exprecine once... and it was I might add a little exciting process..
Sorry for the long response ...