I like to continue down Vancouver, through to Rose Quarter TC. The portion between Broadway and Multnomah is easy. It's a wide street with nary a vehicle in the right lane.
You can cross on the upper deck of the Steel if you feel adventuresome (I never do) by turning right at Multnomah. But I always go straight through the Transit Center as long as there isn't an inspector around to bug me about it. From there I go straight to Oregon Street and Interstate Avenue, where the bridge/esplanade entrance is.
If I had to go around the TC, I might turn left on Multnomah, then right on NE 1st, riding the sidewalk from there to Oregon Street. Second option: After a right on Multnomah, cross Interstate as if to approach the upper deck, then do a 270 into the middle southbound lane of Interstate (or is there a bike lane there? I forget.). Tough one, but probably OK if auto traffic is light.