I need to make it from YVR to SEA by any means except air.
My flight arrives at YVR around midnight; my next flight out of SEA by 7:00.
What is the most convenient and inexpensive way to do this?

Detailed logistics with links would be appreciated. TIA.

there is no convenient and inexpensive ground options at this time.

convenient options, 400 bucks one way.

suspect 1 way car rental is perhaps cheapest.

good luck but this is a tight connection.

Daytime there is hourly airport to airport (plus other major hotels) bus between Vancouver, Bellingham and Seattle. www.quickcoach.com

You are at the mercy of private car or one way car rental at that time of the night.

There is no bus at that time of night

There is a shared ride website but probably no rides that time of day

Maybe offer to drive someone by advertising on craigslist?

This is an insane connection.

I did the reverse, but from a downtown Seattle HLE to a downtown Vancouver HLE, last weekend. I think it was about US$120 + gas.

As others say, none of the bus or train options work in the middle of the night.

Best get on the phone and start calling all the car rental places to see what one-way options are available. Make sure you also clarify their hours to ensure they're open when you arrive.

A travel agent might also be willing to do the legwork for you.

First I want to thank everyone for your advice. Sounds like I need to make some adjustment to my itin.

Car rental does sound like a feasible option provided I pick a later flight out of SEA. Besides, rental places I checked briefly online indicated they don't open until 06:00.

aztimm,
Can you please confirm if your rental was one way. Which company? Any other issues? Thanks.

One-way rentals between YVR and SEA (and vice versa) are not uncommon - I just went to National's site, picked YVR pickup and SEA dropoff and they happily showed me a rate ($100 for an economy car).

Links to the rental car companies at YVR are here -

http://yvr.ca/en/getting-to-from-yvr/car-rentals.aspx

i think this is the one exception north/south where you might find that one ways are not going to break the bank with the airline traffic into SEA and YVR and those that drive north and south from there....$100 bucks is cheap IMO

My SEA YVR one way rental plan is go to all the counters and see who has cars needing to go north or south and then the negotiations starts from there.

This plan might not work for your arrival time as the pricing decision makers are not available to give you a good rate to help them move cars.

I used Hertz. I have a company rate code (whatever they call it). Like I said, I picked up at a downtown Seattle office and returned to one in downtown Vancouver (somewhere off of Granville Street I think). The cost was US$116.80 (just verified, reserved a C/mid size, they gave me F/full), plus gas. I drove 149 miles, @ US$.38/mile = US$56.62. If you rent from an airport, there could be additional fees.
Most US insurance policies work in Canada, so I didn't need that, but you might want to review your policy first.

Generally for one-way rentals, you have to pay mileage/kms, so it could cost a little more.

If you haven't yet, I'd check out the Hertz forum here on FT (and possibly other car rental forums if you aren't tied to one):
http://www.flyertalk.com/forum/hertz-423/
In the Hertz forum, there's a thread about coupon codes. Just plug away until you get the best rate. My company code nearly always works best for me.
If you haven't yet signed up for a car rental program, I'd highly suggest doing so. Along with earning points (this is Flyertalk after all), you can usually avoid the lines at airports and go straight to your car.

Of course if you go this route, don't get gas in Canada, where it is more expensive. The cheapest stations (Sam's or Costco) won't be open at your early hour, but nearly any station in Washington (other than in right at the border) will be less than in BC. We went to Fred Meyer in Bellingham, got some soda, water, and snacks, and filled up there.
But do top off before you drop off and save the receipt, just in case.

I saw something on one forum (maybe it was Hertz?) about Canadians driving rental cars across the border, but it sounds like whatever issue was going on has since been resolved.
I had absolutely no problems driving my rental across. Actually the agent didn't even mention the car. I showed him my passport card, he asked where I was from, how long I'd be in Canada, when I was last there, where I was staying, etc.

That sounds rather risky to me. Just make sure you have a backup plan (ie Amtrak, bus, etc) ready, just in case there aren't any cars available. If you pick this at a peak time and/or when cars are going south for winter anyway, you might be out of luck.

There's typically threads on the car rental forums this time of year about companies giving deals on one-way rentals from locations in the northern US to those in the south. Fall/winter typically isn't peak season for Seattle tourism...