LEAF (Local Enhancement & Appreciation of Forests) Tree Tours are guided walks that take place across Toronto and York Region through the spring, summer and fall seasons. Each tour highlights the interesting trees and natural features of a particular neighbourhood, while incorporating history, culture and personal stories. You can find information about their upcoming tours here.
LEAF also makes available a number of self-guided versions of their past tours, along with maps.
Here's a link to a tree tour they did on Trinity Bellwoods Park and area a few years ago. It's a pdf that's easily printed off for reference while you walk the park and features this wonderful map by Marlena Zuber.