Ok, being a Canadian who has sold cattle to the US, I guess I have most if not all of the information you want. The cattle need to be export certified by an export qualified veterinarian.(they get tagged with steel tags at this time) There are forms, called 12As which have to be filled out and signed by one of the vets at Ag. Canada (food production and inspection branch) district office. Once the paperwork is done, the cattle catch a ride to the States, where the State veterinarian at the border will examine the cattle vs the papers and then allow them to continue. Depending on the distance, the cattle may need to be offloaded to feed and water--it's done in Canada at the Ontario/Manitoba border, various places in the US.....We've used Knills and have been very satisfied with the job they've done transporting the animals we've sold. And we've sold to Ohio, Texas and California, so they've gone fairly far, since we live in Ontario.
If you're still confused as to what you have to do, get the seller to contact Ag Canada (food production and inspection branch) and get it straight from them. I'm fairly positive that the information would be online, but it's sometimes really tough finding the right document on the government site.
By the way, it's a heck of a lot tougher importing from the US since you have quite a few diseases we're clear of (like brucellosis, anaplasmosis, bluetongue....TB too?) Hope this is helpful! V
