One of the CX flights continues on to New York. As well, there is a large expat Hong Kongese population in Vancouver, hence the need for two daily flights with 744 aircraft.
Remember, SIA used to fly into YVR with 743 aircraft, but downgraded to A340's a few years ago. I've heard that most of the passengers on this flight are destined for Seoul, not Singapore. SIA does have traffic rights for SEL-YVR. There just isn't that much traffic to Singapore from Canada as there is to Hong Kong. Maybe the lack of continuing passengers prevent this route from being upgraded to daily.
Are the making money? On the Seoul leg, you bet your ass they are! Any flight from North America to Seoul is jammed packed. SIA's is no exception. I tried in vain to book a flight to Seoul last summer and couldn't find anything from any North American departure point!