There is dinghy sailing available at the Hamilton Bay Sailing Club down near the pier 4 park. They've got a bunch of albacores and might do racing...?
From what I've heard, its run by a bunch of old sailors who don't like change. Not that they're unfriendly or anything.
Royal Hamilton Yacht Club also offers dinghy sailing but more so as lessons... I'm not sure what you're looking for. I keep my laser there and raced last weekend in the Lilac Festival Regatta.
They do Tuesday and Thursday keelboat racing in the evenings. Many boats need crew and it's fairly easy to get onto a boat for the summer.
In terms of sailing clubs at McMaster, I'm currently working to get a competitive club going. There's an Ontario-Quebec circuit starting next year. 2 events in Montreal, 1 events in Toronto, 1 in Bronte and possibly 1 in Kingston.
I'm looking for people interested in being part of a university sailing team, for both racing other schools and learning how to sail. Let me know (msg me) if this is something you would join.
This is what we'll be a part of:
http://canadianusailing.com