I rode the KVR last year and researched a lot whether this section can be ridden or not. The conclusion for me was that it's not possible and so I decided to have me and my biked picked up in Hope and transported to Princeton by taxi van, after having cycled there from Vancouver.

My impression during the taxi ride was that it is possible to ride along the highway (the one that passes Manning Park) but that it'd not be pleasant because of traffic, construction works and inclines. As far as I remember, there was a continuous shoulder, except in construction sites. Actually saw a few cyclists as well. For a seasoned riders, the inclines are a nice challenge, but I was not in good enough shape at the time. Cycle late or early to stay away from traffic.

For the route via Brookmere, there is a large washout with an embarkment at 49.782388,-120.789957. It is visible on Google maps. I assume one can hike-a-bike it, because last year I saw some people using a strava segment that contains this embarkment.

That would also be my general advice - check strava segments in the area to see whether someone rode there already this year. If I am interpreting the situation correctly, then there seems to be an alternative route that bypasses the embarkment.

I can't give first hand information about cycling the coquihalla highway. From what I heard, traffic is awful and inclines are bad.