By default, the metalink redirects you to an appropriate mirror. You can specify individual mirrors, but I do not think you can specify countries. To use a specific mirror, get its URL from here:
https://admin.fedoraproject.org/mirrormanager/
and modify the repository file in /etc/yum.repos.d to use this URL in the baseurl=.. field, and comment out the metalink=.. line by adding a # at its start.