You can go jump at Lynn Canyon right now, but you just can't hit the waterslide and do the main features in the Circuit.
http://mowgli.ca/zones/lynncanyon.html
You can hit 30 foot pool right now, but its cliff are mellow and sometimes awkward.
The stuff down at twin falls might be ok, the Indian head jump is actually better in the early season, but the abyss cannot be hit yet (you will drown).
There is a pool just 30 meters up river from twin falls that should be ok and has a few nice cliffs on it.
Personally, Lynn Canyon is all about the waterslide and given the snowpack, I don't recommend going there until this August at the earliest.
Capilano Canyon has tons of good cliffs and should be good to go right now. I'd recommend going here instead of Lynn at this time of year.