5 hours north of Seattle is Sechelt Inlet and the tiny hamlet of Egmont. A short walk or paddle east of the town is a bottleneck in Sechelt Inlet called Skookumchuck Rapids. This is saltwater whose current can run up to 16 knots and changes directions 3 times a day. If you're unfamiliar with tidal rapids - this is fast, very fast. Some say if you touch the water, if feels like concrete passing underneath you. The rapids can one some days be waist high, and on others overhead - imagine a standing wave peeling and sometimes curling above your head moving at 16 knots - epic. The wave has been popular with whitewater kayakers for years. Sea kayakers have given it a go in recent years, and finally in early 2011 SUPs from I believe Deep Cove Kayak in Vancouver BC began to surf it.
Much like any river, you need to ferry across a thick eddy line (or eddy fence) to get to the 'sweet spot' of the wave. The first wave is prefered, the 2nd is ok, but those in the wave train behind begin to get pretty messy. If you blow your roll or fall off your board, you may have a 1/2 mile ride down the inlet til you can gain control, get into the eddy and slowly paddle back. Many have not been able to paddle back and have had to be rescued by passing fishing boats.
Other tidal known rapids nearby in BC are Oskillo Rapids and Seymore Rapids. There's actually quite a few more, mostly smaller or less powerful. 1.5 hrs from Seattle is Deception Pass State Park which at it's max can run up to 10kts. On a west swell or wind opposing an ebb, standing waves from 2' to 8' can appear. Check my YouTube page for kayak footage of this effect. Even in South Puget Sound last summer, I came across Woodward Bay by Olympia which on the flood created a narrow rush of current under a bridge. I had a good time eddying out, ferrying across, and getting a few 360s in with the sea kayak.
Not much SUP footage exists of 'Skook', but here's one from the Hurrican Riders, a BC based kayaking/sup group. http://www.youtube.com/watch?v=WL2Mq3P9OZ4
Luke Hopkins surfing Skook on an Uli, Here.
Also check out Jeff Burlingham of Medford, Oregon ripping in his Wold Surf Kayak at Skook a few years ago. This is some of the best Skook footage i've seen, nothing short of epic. http://www.youtube.com/watch?v=vxFlj4gw4io
Pic of Warren Williamson and Reg Lake in Sterlings Kayaks on Skook..