well, this fit more on the Language thread, but yeah.
The answer is. Rules of slovak grammar my friend. It is one of the most difficult and complicated grammars in the world. A real nightmare of every Slovak kid However in short, Canada ends with an "A". The suffixes "sko" or "cko" is given only if the name of the country ends with a consonant. for example Francúz - sko, Talian - sko, Bulhar - sko etc...
the names of countries ending with a vowel remain unchanged. India, Ukrajina, Čína, Kórea, Kanada etc... USA for example Spojené Štáty. Kapverdy, Tahiti, Bermudy etc...