Of course not, they're not the same. But we are still talking about a region of about 8-10 million people. It's also a region that has grown by 2 or so million people in a decade. Washington alone has had a pretty steady 14-20% growth per decade since the 60's. Oregon is fairly close in its decadal growth as well. So by the 2030's we might be talking more like 12-13 million people in the region.
That's plenty sufficient density to start investigating if an HSR is economically feasible and advisable.
(Edit: Just for self elucidation, I looked at the number of people that live in the Hamburg - Frankfurt corridor, since that's about the same distance as Portland to Vancouver, BC. Just going off the 'megaregions' that are crossed, its about 20 or so million, give or take a couple. That's only 2x the density of the cascadia region. Berlin - Essen also seems to be about the same distance, and also about 20 million people.)
> Yeah fine, I fully believe in the Vancouver->Vancouver (cough) train line.
At that point, just extend it. Put a bridge over the river and have a train terminal somewhere near PDX. The further continuation into Salem and Eugene is a little iffy, that I will concede, but Vancouver WA to Portland is practically spitting distance.
However, I will also note that factors are 2 are far larger than the ones that often make or break social or economic plans. So saying "that's only 2x the density of Cascadia" is not necessarily very encouraging.
The justification for it, however, is not "WA is just like Germany".
First of all, it's gone to be a relatively single-line system, paralleling I-5, which is quite unlike Germany,
Second, even with the full west-of-cascades population, you're still not even remotely close to the population of Germany. You not even really that close to the population along any of the busiest lines within Germany,.