As a Boise native and Portland resident, I have a few observations.
Boise is a great place to live, however, it is the most remote city, in terms of it being close to a major metro area. It's a little isolating and people who live there tend to get a "Center of the Universe" mentality. And it's very Mormon-heavy, meaning just as much as Salt Lake City. I had many Mormon friends, but it will dominate Idaho politics and sometimes your daily life. If you're conservative, you probably won't mind. I was born and raised there, stayed in-state for college (but not in Boise), but had ZERO desire to return there for living. But overall, it's a good place to raise a family, has better public schools than Portland and a plethora of outdoor activities. The people are far nicer in Boise and strangers do say hello. Not so much in Portland.
Boise has very hot summers (think 90-105 most days in July/August) and winters can be sunny, but the city gets locked into an inversion for weeks at a time, typically in December and January. In fact, Portland has had far more sunshine this winter than Boise, which isn't common, but don't believe Boise is always sunny. It ain't. And it's really brown and arid when you compare it to Portland. But if that's your thing, go for it. I love the green of Portland and the lack of ice and snow (except for this week's snowpocalypse). The summers in Portland can't be beat anywhere. Unless you hate 85 degrees, sunny, green and few bugs.
Portland has a much better food and arts scene, if you care, as well as major pro sports like the Blazers and Timbers. And if you want your NFL or baseball fix, drive a few hundred miles to Seattle. Boise has "Boise State University" which is a mediocre commuter school with a good football program. Portland has just so many more options than Boise. But if you don't get out much, it won't matter.
That being said, I think Vancouver could be a good choice if you have the opportunity not to travel to PDX during rush hours (a terrible, terrible fate). It's certainly one of my options, if I reach FI and want to stay in the area, to move to Vantucky for lower taxes and a more quiet lifestyle with Portland's attractions nearby. Downtown Vancouver, albeit a little underachieving, has shops and restaurants and bars. It will continue to get better and better.
Both cities are good places to be, although I would take Portland every time. Good luck!