Most people I know who swim open water in B.C. (I don't!!) have long-sleeved wetsuits...

These are photos of a recent Vancouver Triathlon (sept 07):
http://www.pbase.com/markcreery/vancouvertri07

You'll find some sleeveless racers, but most people, including the leaders, wear sleeves it seems.

Perhaps you'd make it with a sleeveless, but you'll get more versatility out of a longsleeved I think...