There is no immigration class just based on having studied in Canada for x years. There are however options for phd students, in some cases for masters as well as for any students who graduates a 2 year or longer college or university and then works a skilled job for at least 1 year full time. That last one would be Canadian experience class. Look at http://www.cic.gc.ca/english/immigrate/index.asp for your immigration options.
