I used to sail my Bravo and Adventure Island in Lake Ontario. There are a lot of days where it's not so bad out there, even for learning, just dress for the cold water.
I'm going to be doing some sailing at Belwood Lake and Guelph Lake, both of which have small boat sailing clubs.
Here's a link to Belwood Lake. The launch area is just to the west of where 4th line ends. If you zoom in, you can see it. The sailing club is tougher to see on Google Maps, but they launch just north of where the public launch is.
http://g.co/maps/e4fgcIt looks small on the map, but here's a video taken of their sailing club last year (I found it online) this is in the south narrow part of the lake, and you can see there's plenty of room to get around, and the sailing club seems to have at least one active Hobie Catamaran, and I've seen a few more out there.
[youtube]http://www.youtube.com/watch?v=DFqJ8Oce_d0[/youtube]
Following is the Link to Guelph Lake. I haven't been there yet, so I'm not exactly sure of their launch area or anything else.
http://g.co/maps/zt9af