Why not buy a Amsterdam to Toronto, returning from Vancouver ticket? (Often called an Open-Jaw ticket)
The price would be similar to an Amsterdam to Vancouver return, but you'd fly into Toronto and back from Vancouver, booking your own train tickets for the Toronto to Vancouver leg.
For the train from Toronto to Vancouver, it's "The Canadian", and you should be able to book that online beforehand. See the Seat61.com page for more info on the train (though the viaRail site is pretty good too)
Most airline websites will sell you an open-jaw ticket, but you normally need to go through their multi city booking interface to do it.
