Depending on how enthusiastic someone is about pursuing ownership records, the New Westminster Land District (which covers the majority of the Greater Vancouver area) does have this information available. It involves actually going into their offices to start the process, and they will not give out the current ownership information without the owner's permission or pin codes. Historical information is available, but from personal experience, the route that sami is suggesting is far easier and is available online up to the early 1950's. Unless you need to know exactly who "owned" the property, the folks that lived at any given address for most years can be determined.
It would definitely be helpful to have the address of your Union Street relatives...
