I cannot say whether you should plead guilty or go to trial as that is a decision you must make. However, I can give you as much info as possible such that you are able to make an informed decision as to what course of action you wish to take.
Firstly, as you may know, the Tobacco Tax Act is not criminal legislation. In other words, if you plead guilty, you will not have a criminal record, but rather merely a provincial / regulatory offence conviction- similar to a speeding ticket. Thus, pleading guilty will not result in a criminal conviction, which is obviously very important.
However, pleading guilty will, as you know, result in a fine. You can certainly try to speak with the prosecutor, inform them of how you are a good person and aside from this isolated incident a contributing member of society (e.g. employed and/or educated). This may lead the prosecutor to offer a better plea deal e.g. lower fine. You could hire a lawyer for these negotiations though that may end up costing you more than the amount of fine you save from the lawyer's work. So, if you do ultimately plead guilty, though hiring a lawyer would be helpful, it's not overly critical.
If you wish to go to trial, success may be difficult as the courts that hear such cases are generally more favourable to police and government agencies than they are to the individual accused persons. As such, if you intend to fight the charges, hiring a lawyer would likely be ideal. That being said, if it's a very difficult case to win (e.g. they clearly caught you, cigs couldn't belong to anyone else, and the search was lawful), then pleading may be a better option since it will save money and chances of success at trial in any event would be dim.
Hopefully that is of assistance.