One way to walk in to the mouth of the Wallace is to drive to Startup and turn right on the road by the store and cross the river. Follow that road for several miles, and when you get to the point where the road makes a sharp right turn and there is a road to the left over the railroad tracks pull off and park by the tracks. Then walk down the tracks towards Sultan and you will eventually come to the mouth of the Wallace. The last time I was in there last year I couldn't wade to the "island" due to high water but sometimes you can.
Another way is to drive into the housing development around the Wallace mouth. It's a couple roads up from the road over the Skykomish at Sultan. Then you can hopefully walk in to the hole. The problem is that here you're on the wrong side of the river and there are lots of no trespassing signs. Homeowners don't seem to steelhead friendly here.
Or, you can park at the area on the far side of the bridge over the Skykomish in Sultan and walk back across the bridge to the highway side. Then go down the bank to the river and walk up river along the gravel bar. You can walk all the way up to the houses along the river at the mouth and get some fishing that way. Not sure how far you can go without running in to posted property this year.
I haven't tried this one, but looking up river from the bridge over the Skykomish at Sultan it looks like there is now a decent sized gravel bar on the South side of the river. It looks like it you parked in the DNR area and hiked across that field you could come out by the bar and it might be good fishing.
One good thing is all these methods will get you a good workout and fresh air, and if you decide to keep a fish take a stringer to help carry it out.
I still have yet to see a winter steelhead on either the Skykomish or the Snoqualmie. I'm going to look and see if the tribes have nets down in the Snohomish when I get time. If they do that might mean there are fish in the river.