Salmon fishing has ended until next summer.
Every stream in the Lower Mainland and Fraser Valley produce
cutthroat trout,
rainbow trout and
bull trout, some are just more productive than others. Squamish River, Cheakamus River, Stave River, Chilliwack River, Chehalis River are just some of the larger systems that are worth trying. There are of course smaller, more intimate systems as well, such as Little Campbell and Serpentine in Surrey, small North Lower Fraser tributaries between Mission and Hope.
No specific spots are mentioned for a couple of reasons. One being spotlight of specific spots generate crowding, a concern which you've already addressed. Two being these species are more mobile than salmon in streams, so more emphasis should be placed on how to hunt for these fish than where to stand and wait for them to find you.
These three species are mainly focusing on loose salmon eggs that are drifting off redds and pieces of flesh from carcasses. Whether you are flyfishing or float fishing with gear, egg patterns or big pieces of flesh patterns produce well. We've also done well by casting and retrieving small spoons. Just because they are feeding on specific food items, it does not mean other presentations would not produce, just not as much.
Good luck.