In Vancouver best bet is to go down to the Yacht club by the Burrard St. bridge and find out what day race
day is (usually Sundays at most clubs). Linger around before they do the race meeting and offer up yourself as extra crew. Might take a few tries before you get aboard, but once you get aboard once, if you're allright, when you hit the after-race drinks with the rest of the racers you'll find you can get aboard quite easily most weeks.
Having good English
will really help, I find that most of the people I meet from that Yacht club are multi-generation Canadian native English
speakers - and since being crew requires good communication if your English is choppy it may be more difficult to get aboard that first time.