It is very difficult to adopt a family member even if their parents are dead because there is so much attempted fraud. Usually the child is expected to remain in their home country. The country of origin seems t also make a difference.
In theory yes. This assumes that you adopt the child, the adoption is both legal and acceptable to Canada. IRCC will heavily scrutinize the application for "adoption of convenience" or fraud. However, your being married is not a factor if the adoption route is followed.