You can post in US or CDN. It's up to you. If you are not an Ebay member, you will have to register. Follow the steps on the registration screens and once registered you can place your items up for auction. Just follow the steps in self-explanitory.
Your item can be viewed by people in US, CDA, Nether,GB..etc.
I think once you put it what catagory your item is going in Ebay automatically place in the car parts section..just check on Ebay. I've bought and sold items off it.