You can check availability using the United Airlines website. This may not exactly match availability via SQ, but it's usually a good guide.
To calculate the number of points required, you can check the Star Alliance award chart on the KrisFlyer website. You'll need to call SQ to get a quote for the taxes (and to book) but in my experience they're pretty reasonable for Air Canada bookings originating in Australia. I think it's around $100 one-way in taxes for the BNE-YVR flight.