swapnochary,
if you want to take more stuffs then China Airlines (operated by Taiwan) is the best for you. Their fare is cheaper than others. You'll have to go to New Delhi or Bombay from Dhaka and then to Taiwan and then to Vancouver or Toronto over the Pacific. They allow 2 pieces of 32 Kilos each and a hand luggage. one of the BD guys did travel using China airlines, Cant remember his name.
Apart from that, your best route is Emirates. From Dhaka- Dubai-Toronto(14 hours non stop).
You can However choose Qatar Airways, Singapore Airlines ( They have Vancouver over the Pacific), Thai Airways, Kuwait Airways --- all of them have Transatlantic flights connecting Heathrow and then to Canadian cities in Air Canada.