As long as you are sure you are dealing with Quebec immigration people, it should be safe. One prudent step would be to make sure the credit card numbers can't be seen through the envelope - use a security envelope (with extra printing on the inside), or maybe paying attention to how you fold the sheet would be enough.
While I don't think this is an issue with student visas, do be aware that there are some people out there who offer to "help" immigrants by charging high fees for unnecessary services.
Remember that it often takes just as long to do a search or two on Google to try and find the answer to your question as it takes to type it in a post here, let alone the time waiting for a reply.
If your question is "What mark does it take to get into University X", or "What are the requirements to get into University X", it's on their website and/or
electronicinfo.ca (for Ontario schools). Particularly for Ontario schools, those ranges are a pretty good picture of what kind of mark will get you into the program, and if you're more than a couple percent higher it's practically guaranteed unless it requires a supplementary form.
