The Vancouver Waterfront has become a great place for long level walks. Several new portions of path have been added, but one section, immediately east of I-5 has deteriorated and been closed to access. Still, there is another route and just under 2 miles of connected waterfront walk.
I feel the best place to start a walk on the waterfront is on Columbia Way just east of I-5. From here you can walk along the river either east or west, or you can cross Columbia Way and visit the Old Apple Tree, the Confluence Land Bridge and Fort Vancouver.