Best way: Taxi or your own car.
Other ways:
Walk or monorail to the TTC. Take Epcot monorail to Epcot. Walk all the way through Epcot Future World (you must have a ticket for this) and out the back of the World Showcase to the International Gateway. BC/YC are a 5 minute walk from there.
Take the bus from the Poly to DHS. From there, either walk or take the boat to BC/YC.