In case anyone is interested, Vancouver - Bellingham isn't technically the SLOWEST part of the Line... that honor goes to Everett - Seattle. However, it's slowest for the longest period... by far:
It averages 48km/h for 100 km. Granted, a small part of that is because of the border crossing, but still, it's pretty slow.
Entering Seattle, it averages 46km/h, but only for 29km/h.
The fastest part of the line is all South of Tacoma, with Kelso to Vancouver, WA being fastest averaging 102km/h, for 64km.