Ontario has inspired a rich body of nature writing and field guides, particularly around its exceptional birding, botany, and wilderness areas. These are worth picking up before you head out into the province's parks and forests.
Forest Plants of Central Ontario by Brenda Chambers, Karen Legasy & Cathy V. Bentley (ISBN: 1-55105-061-7) — A solid field guide for identifying the trees, shrubs, and wildflowers of Ontario's mixed forests.
Wetland Plants of Ontario by Steven G. Newmaster, Alan G. Harris & Linda J. Kershaw (ISBN: 1-55105-059-5) — Detailed coverage of Ontario's wetland flora, useful anywhere around the Great Lakes shoreline.
Ontario Birds by Chris Fisher (ISBN: 1-555105-069-2) — A compact field guide covering the province's most commonly seen species, good for Point Pelee visits.
Animal Tracks of Ontario by Ian Sheldon (ISBN: 1-55105-109-5) — Handy pocket guide for reading what's been through the woods ahead of you.