Hi,
I took a Greyhound bus from downtown Seattle to Vancouver with my wife a few years ago because I had Southwest free trips to use and the closest they go is SEA. Spent a few days in Seattle first so took a supershuttle type van from the airport to downtown hotel.
Trip up to Canada was very nice, clean bus,left and arrived on time.
Return trip was pesky because if anyone on the bus has trouble at US immigration/customs, the whole bus waits. Not sure on the Greyhound policy on how long they wait before leaving the person(s) behind but in my case we waited for 2 hours. This was pre- 9/11 .
Steve