Cedars is not accessable by public transport as it is a good 20 mi south of the downtown core. St hubert is probably your only choice. How hard it would be to get to would depend on where you are starting from. Montreal does have an excellent Metro ( ie tube ) system. I got my PPL at Cedars in the 1970's and even back then it had a definite advantage over St Hubert by virtue of being out of the Montreal terminal airspace. You might try the Canadian Owners and Pilots Association for more info. They have a web page.