PR entering Canada with a different passport-implications?

[wahwah]

Hello,

My sister's family are re entering Canada permanently next month. They landed in early 2009, got their PR & SIN cards, then went back to their home country because of family reasons. Recently, her son gave up the citizenship of his country of birth to take up the citizenship of his mother's country. On behalf of my sister we would like to find out whether her son has any problem re-entering Canada next month for his tertiary studies using his new citizen's passport since his PR card which expires early 2014 indicates his former nationality (country of birth).

Many thanks for reading & your comments!