Did you know that it takes about the same amount of time to fly from London directly to Toronto than it does to fly from London directly to Vancouver?
It doesn't look that way!
On a map Vancouver looks like it's twice as far away from Europe than Toronto is, but it isn't when you take into consideration the curvature of the Earth.
Flights from London to Vancouver don't fly directly west over the Atlantic, as if you were drawing a straight line west out of London. They arc north up and over the Arctic (har har), over Greenland, Baffin Island, Nunavut before descending over northern Saskatchewan, Alberta, eventually ending in BC.
While it still looks like a further distance on a regular map, if you traced this route on a globe, it would make more sense. It's that Arctic route which explains why flying directly from Europe to Vancouver makes more sense than flying with a stopover in Eastern Canada.
London to Toronto = 8 hours
London to Vancouver = 9.5 hours
Toronto to Vancouver = 4 hours
London to Vancouver via Toronto = 12 hours
As for people flying into Vancouver from other destinations, Tourism Vancouver has created a fantasic PDF illustrating the average flight times from around the world: