You need to find an award on one of the UR partners before transferring. There is no set value for the mileage programs (except Southwest), so it depends on what you're using them for. It's possible you could transfer to United and get round trip Vancouver-London for 60K flying on Air Canada. Go to united.com and plug in your route and dates and see what's available and for how many miles. Saver level awards will be the best value, and probably the only ones worth doing compared with using the UR for direct booking as you mention.