Read other threads here. Basically the youth would apply for a PRTD (pr travel document) on basis that was removed from Canada as a minor and now is attempting to return at first realistic possibility. (Could also travel to usa and present at border and take chances there). I'm assuming prtd is most likely i.e. child does not have/would need visa to usa.
No-one can say what chances are that prtd will be approved. Factors that would be considered are age, attempt to return, ties to Canada, etc. (Eg chances might be better if child spent much time in Canada and was schooled there, less if only ever spent a day in Canada.)