For those of us in Canada, typing "ca" should probably rank countries that start with the "ca" prefix first, followed by countries that have a word that starts with "ca", finally followed by countries that just happen to contain "ca".
I don't see much use in showing "United States" as the first match for a user who has typed "c" and "a".
The same problem exists for the prefix: "uni". The list in that case is:
United States
United Kingdom
Réunion
Tanzania, United Republic of
Tunisia
United Arab Emirates
United States Minor Outlying Islands