I know someone who tried to do this with a one-way ticket from Europe to the USA. They were denied boarding in Europe (pre-immigration screening) until they purchased, on the spot, another ticket out of the USA. That being said, it sounds like you will have a ticket from Vancouver to Bangkok which should give you a stronger argument.
In my experience these rules are not clearly defined and often arbitrarily enforced. In the situation above, the last-minute ticket that was purchased to satisfy the onward travel requirement was a fully refundable ticket that was then canceled and never used. In fact the pre-immigration officer in Europe basically recommended this as the simplest solution and then let the passenger board basically knowing that this last-minute ticket was not going to be used.
When I crossed the border Canada -> US (on a European passport) earlier this year by car they did not ask for any return tickets. Just what I do for a living, how long I plan to stay in the US, how I plan get out and how much money I had on me and available in my bank account.
Been there before for 2 weeks and in transit a couple of times; so maybe they took my previous records into account…
The first time however was a completely different story; had to attend a conference, but did not book a hotel before and the guy in customs wouldn’t let me pass until I had an hotel address for my arrival card. Was stuck there for ~1h, in the end I just wrote down a random hotel address from the yellow pages.
So my advice would be to have some sort of reservation for a hotel/hostel where you stay for at least one night, and the greyhound tickets just in case, because you MUST write some address down on your arrival card, otherwise thou shall not pass …
Yes, have all the documentation of your travel prepared for each leg! Outline your trip briefly to the officials, explain that it was most cost-effective solution and show him/her that despite the fact that you have a one way ticket, you’re leaving the country on X date. I think I’ve heard it’s also helpful to have any other supporting documentation — i.e. reservations at hotels/car reservations at the third locale as extra supporting evidence.
Credit:stackoverflow.com‘