Regarding the way the imposition of a minimum sentence is announced, the prosecutor must give notice. In fact, the requirement to give notice is contained in section 727 of the Criminal Code. This covers all cases involving minimum sentences. If a prosecutor intends to ask for a minimum sentence for an accused, the prosecutor must give notice. The prosecutor must also indicate to the court that the notice has been given.
Regarding the type of conviction, it is only limited to this offence. For example, offences committed by an individual which are covered by the 2001 Excise Act will never count. So that issue is dealt with separately.
Regarding the disparity between the practices of the prosecution from one region to another, you probably know that prosecutors have fairly wide discretion. Generally speaking, this discretion is more or less exercised based on the region you are in. If the problem is much more serious in one region than another, it is possible that more minimum sentences will be imposed. I am not concerned about that. This corresponds fairly well to the usual discretion the prosecution enjoys.