Ok, I found an interesting tidbit of info last night at work. *runs upstairs to get it*
Raptor, have you ever heard of evergreen.ca? I came across a flyer for it last night at work, and instantly thought of your tree planting idea. By far, I think this is the best resource for your plan for spring.
Welcome to Evergreen /en/ This is the main site link. Some good info here.
Evergreen - Project Registry This link lets you register your volunteer project.
I'm sure this site will help you to plan this event for the spring.