I would start by grabbing a copy of the Clark County bike map (http://www.clark.wa.gov/public-works/bikepath/Bike2007.pdf). It's a little old but useful. One thing to note about Vancouver - Streets run east-west, Avenues run north-south. Can get a little confusing sometimes but this holds true for all of Clark County.
If you want a direct route I would head over the I-205 bridge, follow the path west onto SE 23rd which ends at Ellsworth. Take a right and go up the hill to SE 10th St. Go right at the light here, stay straight (it changes names to McGillivray at Chkalov). Follow McGillivray to Village Loop. Go left and take another left on SE 160th Ave (changes from SE to NE when you cross Mill Plain). Stay on this until it curves around to 162nd Ave. Turn left on 162nd Ave and follow it north to Ward. I would take NE 172nd/170th Ave north toward Battle Ground, where you could pick up NE Risto out to Venersborg.
Another option (with more miles) -- you could follow the RACC route on McGillivray, which takes you past Lacamas Lake, and eventually dumps you at NE 164th St and NE 182nd Ave. I'm not sure about riding that stretch of 182nd north to Venersborg but you could follow the RACC course to NE 170th Ave. Much of Clark County has some nice roads, though shoulders can be scarce in a lot of places.
Steve