Where can I get cheapest airfare from Singapore to Vancouver (round trip)?

China Airlines (Taiwan) typically has the lowest fares from N. America to most destinations in Asia. You also might want to check Oasis Airlines, which has great fares to Hong Kong and then search for a good fare from there. EVA Airways also usually has good prices to Asia as well. Airlines like Cathay Pacific and Singapore Airlines are probably the two best airlines to Asia, but are normally more expensive, but sometimes offer great specials. Good luck.