Four provinces, Quebec, British Columbia, Alberta and New Brunswick, as well as Yukon, have legislation specifically providing for grandparent access. Other provincial legislation as well as the federal Divorce Act allow for access applications by people other than parents without explicitly mentioning grandparents.
US (also from the above link): Grandparents can petition for visitation but it had to be in the best interest of the child, i.e. established relationship plus other factors. "Fit" parents are generally given the right to decide.
Not sure about other places.