As a responsible outdoorsman and advocate of all things safe, I of course advise against going off the trail. Not on ly is the risk of tripping and falling way higher, ubt you also expose yourself to encounters with wildlife that could be displeasing and counter-productive.
So anyway, I went off the trail in Lynn Canyon park.
The only problem with the North Shore canyons is the lack of light. Shooting over 1/50 is frequent. Tripods are a must (even on sunny days, sadly), which makes the scrambling over wet rocks and mossy trees a little harder than it should be.
Most of the park is actually pretty dangerous. The huge cliffs leading down into the canyon are unforgiving, and Metro Vancouver is pretty explicit about it. There are, however, areas where it is relatively safe for someone loaded with gear to make their way down. Hiking east of the bridge, for example.
The one advantage of shooting in permanently overcast, grey weather? It makes the water look sharp as hell.