As per the above link posted by barons a dangerous driving charge/conviction will make him inadmissible to Canada. You will have to look at what will be needed in order to make him admissible again.
If he end up with a conviction that makes him inadmissible, he will need to wait five years from the time he completes any penalties associated with the conviction (e.g. pays any fees, completes any programs / probation) - then he will have to apply for rehabilitation. Once rehabilitation is approved - he'll be admissible to Canada again.
