If we want to make it just a one day event we could get a sheltered group picnic area at a city park. We just have to decide what city and then book a spot. Permits are usually in the $50 - $75 range but sites are first come, first served so if there are any good spots left we would have to act soon. Toronto has dozens of parks with hundreds of group picnic areas.
I doubt we could do any kind of overnight event this year. When I planned my family reunion I had to start looking and planning a year in advance. If we want to go to a nice place (like the Lion's Camp in Dorset or one of the better Girl Scout Camps) the bookings are up to 2 years in advance. Plus, it would have to be held in spring or fall because these camps are in use by their groups in the summer.
We have to decide to just do it - pick a date, book a spot, make the announcement & send out our invites! If we build it, they will come!!
As they say in NASCAR - "Git 'Er Done!!"