In most cases, following a successful judicial review, your case is sent back to be re-determined “de novo” (meaning “as if it were new”) by the decision-making body (but usually a different specific decision-maker). The record from your previous case will still be in front of the new decision-maker, unless there is a specific reason for it to be excluded. However, you will also have an opportunity to present new arguments and evidence.
Sometimes the law will be fixed at the point at which your case was originally filed or decided. For example, if you were eligible for a program when you were refused, but are no longer eligible, the case may be redetermined as if your eligibility was “frozen” during the previous application (this is often the case, for example, when dealing with dependent children who were young enough to be sponsored when a case was originally refused, but passed the age limit during the Federal Court case). However, not everything is fixed. For example, if during the Federal Court case you have obtained a criminal conviction which renders you ineligible to come to Canada, the decision-maker won’t overlook that.
Having your case redetermined after succeeding at Federal Court can, unfortunately, take almost as long as the original case took to decide; this depends very much on the kind of decision being redetermined.