You can contact the schools to get a letter of acceptance by yourself and then prepare all the documents for the students visa application.
Usually the consulting fees is about USD2000-USD2500. But it depends on different situations...
Cinic, thanks for your answering my question. I still wonder if you know any Secondary schools in Montreal that can accept international students. So grateful for your help!
To find a school is not a problem. But I think generally Canadian Beijing Embassy doesn't issue the student visas to the students who won't finish their high school before they go to Canada.