[twoNeurons]

Okay: More info I gathered from the WSDOT's Long-term plan:
Page 46:

Currently (2006) from Bellingham:

To Seattle: 2:25 ( ~170km of rail )
To Vancouver: 1:48 (~100km of rail)

Mid-point Goal:
To Seattle: 1:59 (26 minute improvement)
To Vancouver: 1:39 (46 minute improvement)

2023 Goal:
To Seattle: 1:44 ( 41 min. improvement total)
To Vancouver: 0:50 ( 58 min. improvement total)

Average Speeds:
BEL - VAC:
Now: 56km/h
Mid: 60km/h
2023: 120km/h

BEL-SEA
Now: 70km/h
Mid: 85km/h
2023: ~100km/h (this includes station stops)


These speeds are average, and obviously VAC - BEL will be faster as there is only the border.

The planned maximum speed is ~175km/h (110mph)

Currently, trains are legally limited to ~127km/h (79mph)

Without building dedicated tracks, that's probably the best we'll do, but as you can see, most of the upgrading would appear to be on the North side of the border.

The biggest improvements coming after building a White Rock By-pass and Colesbrook - Brownsville High-speed track(Surrey) [p. 105], which, combined with Improvement south of the border in Mt. Vernon, Bellingham, Blaine and Everett, will shave 50 minutes off the trip length.