Form IMM 5490, question 8, asks the sponsored person to list all relatives living in Canada. It's because having a lot of relatives, especially close ones, in Canada is considered a 'pull factor', something that might make a foreigner want to come to Canada and try to do so by a fake marriage. Don't worry about it if you do have relatives in Canada, though - it is just one of many factors they look at.
If the sponsored person has no relatives in Canada, knows no one in Canada besides the sponsor, can't speak English or French, and has few transferable job skills, the visa officer will be inclined to think that the sponsored person will in fact be going to live with the sponsor once a PR, and so therefore the marriage is genuine.
The judge at my husband's appeal wrote in the decision that even though my husband has no contacts in Canada other than the sponsor, the fact that he speaks English and has extensive business experience means that he could establish a life for himself away from the sponsor. In other words, I should have married someone who couldn't speak English and had no way to make a living. Damned if you do and damned if you don't.