Toronto - picnic + RAIN?

You did not mention how many people would be at the picnic, but since you say "lots" of food, I'm guessing more than a dozen.

If it rains, there are some buildings on Centre Island you can seek out for shelter. The Hong Kong Pavillion is a covered area that you might be able to go seek shelter under, and there are places like the St. Andrews-on-the-lake and a few other places.

http://www.naisa.ca/soundtravels/2004/Images/pavil...

However, I doubt that they were designed to be used by picnic'ers to host their events, and so you probably would not be using a BBQ there or setting up tables and eating. You also would have to compete with probably a bunch of other people caught in the rain for the space.

Your best bet would be perhaps to get one (or more) of those gazebo/suntents that are sold at Canadian Tire. Yes, they may be expensive if it's just for this event, but consider how ruined the event might be by a downpour, and after this picnic is over, you could still have the tents for any future outdoor event.

http://www.canadiantire.ca/AST/browse/5/SportsRec/...

Another option is to go to the nearest equipment rental place. Many of them rent things for parties, including a really large tent for parties. Of course, you will want to find out if the Toronto Islands Parks will allow you to put up a temporary structure like a gazebo or party tent, as they may have restrictions for that.

When I use to go on picnics or have one I never let the rain ruin it.