There are 54 members of the Commonwealth, a loose association of former British colonies.
Western nations have been pressing Sri Lanka to account for thousands of civilians who are suspected to have died in the final months of a quarter-century civil war that ended in 2009 when government forces crushed Tamil rebels who were fighting for an ethnic homeland.
While Sri Lanka has enjoyed peace in the past four years, rights groups have accused the government of squelching dissent and suppressing the judiciary.
Australia and Britain have pushed for engagement with Sri Lanka rather than isolating it, and have encouraged countries to participate in the Commonwealth leaders' meeting in Sri Lanka. Several human rights groups have urged a boycott.
Harper said Canada will also examine its financing of the Commonwealth. He said if the Commonwealth is to remain relevant it must stand in defense of basic principles of freedom and respect for human dignity.
Canada contributes about $20 million annually to various Commonwealth initiatives.