I want my site to appear in the search results for the US, UK and Canada only. Currently I am getting a lot of traffic from other countries and they are taking up my bandwidth. The service I offer is not available to other countries. Is this possible?
No I don't think this is possible. You just have to work at increasing traffic in your target regions. You can do this by concentrating on building links on sites hosted/targeting that region. I'm sure you could setup an ip detecting script that forwards users if their ip does not match your target country. Really you should just accept that you will have some international traffic. If it is too much burden on your server, then you likely will have to upgrade.