Several parts of this route are very confusing until you have done it once. Bring a map and allow LOTS of time your first ride.
On the map above, you want the green line that goes through Delta Park. As you leave Delta Park, the road ends, ride through a fence, cross a ramp intersection and then turn left on a bike path to head to the I-5 bridge (after several more confusing turns).
Once in Vancouver, consider going N to Evergreen, to Fort Vancouver Way, N to McLoughlin, E to Grand, N to 18th, E to General Anderson. Bike lanes most of the way, some brand new.
Also, the Hwy 14 land bridge is supposed to open by early or mid 2008. See the purple line on the map above that goes through Fort Vancouver and over 14. That will be a shortcut up to Fort Vancouver Way (via 5th). Picture of bridge below.