It's quite possible that Edward and Elizabeth died prior to 1900, which is the next available census--the 1890 US censuses were lost in a fire.
Have you searched for their death records, obits, or burial places? (You may want to post a request on the Conn. board since that's their last known place of residence.)
Have you been able to find any of Edward and Elizabeth's children in 1900? Elderly parents often live with their children, so if they were still living, they may be with one of them.
Have you searched for Edward and Elizabeth in Canada, before and after their marriage? If you don't have an international Ancestry membership, try Family Search. Their marriage record should contain the names of their parents, then you can look for them in Canadian censuses to get the names of their siblings.
In my opinion, I'm not sure that creating trees for people you aren't sure are related to you will help you connect them to your family. I think you first need to find the names of people who you KNOW are related, then see if they appear in the records you collected 15 years ago.