The Home Depot
Home Depot Canada has a monthly budget that goes towards donations. Whatever is their featured charity goals for the year through their The Home Depot Canada Foundation, will take president. If there is any funds available after that they will help other non-profits and charities.
On your letterhead, addressed to management, deliver a letter to a Home Depot closes to you. On it outline who you are, what materials you need and why. Good luck!
One tip given, is if yourself or a volunteer sees a construction site in your area, to stop and ask. If there’s any products left over when the project is done, they might be open to donating it to you if you pick up.
Lots of these left over materials end up on the garbage dump, and there are some organizations trying to minimize this waste, pick it up and re-sell. So if there’s nothing already in place you might be able to get some lumber or other materials donated.