Our recommendation would be that parents whose children are all living in Canada should be on a priority list, because they don't have other children living with them back home. They need care the most.
There are other things. Parents are a lot closer to a child than are siblings or grandparents. So they should be on the priority list, rather than grandparents or other siblings, like brothers and sisters. So parents who don't have any dependent children should be on the priority list.