It's a bit out of the way to get down to McMenamins, which is almost just off of the Interstate bridge. If heights are your main concern though, the bike path on the I-205 bridge is sandwiched between the opposing directions of traffic, keeping you a good 60 feet from peering over the edge. This makes for a rather loud ride, all while cycling uphill for two miles.
But to answer your question, there is a bike path across the I-205 bridge. To get on it heading north, just follow the I-205 bike path north past Airport Way and take a left onto the bridge. From Vancouver, it's accessed from SE 23rd Street, just off of Ellsworth Road, just south of SR 14.
Gas Tax Holiday? I must be on gas tax retirement.