First off, you are very lucky to live near the Selkirks. I often look at real estate in northern Washington as I approach retirement. I currently live in northern Colorado, so I do count myself very lucky.
Yes, I would think it would be very hard to "freeze" this waterfall without any direct sun on it. Typically you don't normally freeze water in a waterfall, but in this digital age, it wouldn't hurt to try if the conditions allowed it.
Your image looks fine the way it is. If your shutter speed is a few seconds, then it's understandable that there will be some movement in leaves and/or needles if there is any wind. I don't stack or merge images so someone else will have to help you there.
Do you have a neutral density filter? If I have a one or two second exposure of a river or waterfall, I'll also throw on a 6 stop ND filter to see what it looks like as a one or two minute exposure.
On a side note, your image might need to be rotated a few degrees clockwise to level it out.
Also, I think it would be cool if we could post troublesome RAW images and let other photographers on the site work their magic on them.