By train To get there from Montreal if you do not have a car, the easiest approach is to take the AMT commuter trains from Montreal's Gare Centrale (Central Station). Prices and timetables can be found here, and it should cost around $8 each way. As the local train station is around 4-5km from the trailhead, the most effective means to get there is to hitchhike or take a taxi.
By bus * CIT Valle Richelieu  serves McMasterville, St-Hyacinthe, Beloeil, and Mont-Saint-Hilaire. See the website for schedules.
The hiking is at McGill University's Gault Nature Reserve, and should cost around $5 per person.