I'm assuming you work in some sort of law enforcement capacity, and you weren't in a holding area as a "customer". ;D
What I would do is: Contact the police officer who made the arrest, if you know their name. If you don't know their name, the police department main number should be able to tell you which watch was on at the time in question, and then you can contact the watch commander to find out which officers handled the call. It's unlikely you'll be able to influence the officer's decision to lay charges or not, especially if it's just because you want to avoid being a witness as you'll be in the CF by then and be elsewhere. You can't really approach the Crown prosecutor until you know whether charges have been laid or not, because if they haven't, the Crown prosecutor won't have a file on the matter.
That said, if they do lay charges, and it goes to a Crown prosecutor with you listed as a witness, it'll likely be months before an arraignment. If you've joined the CF and are elsewhere (doesn't matter where, really), then it becomes the problem of the Crown to serve you with a subpoena to appear for trial. If they can't serve you, then problem solved, and the charges will eventually end up being dropped against the guy. If you're across the country, and they manage to serve you somehow, then you can deal with the Crown prosecutor to explain your predicament being thousands of km away and working for the CF, and it'll be his discretion as to whether he wants to pursue the charges or not.
Make sense?