I'll answer your question with a question: How high is the sky??? The answer: who knows? Deployments come and go at the drop of a hat, on the whims of the current government, and more precisely, the world situation. There are so many "almost" tours that people were all trained to go on, and then the mission faded away, because peace broke out in that country (or our government changed it's mind). On September 10th, 2001, I don't think anyone in the CF thought we would have troops in Afghanistan less than 6 months later, but guess what happened? Haiti (pt II) came up pretty quick, and is ending at the end of the summer. Bosnia isn't even a "gimme" anymore if you are in a field unit, as the manning for that is dropping big time.
There are people who have served more than 20 years in the CF and haven't gone overseas once, and others with less than 10 years in that have been on 4 or 5 missions. A lot of it is "right time, right place" (or wrong time, wrong place, depending on if you never got a tour, or far too many..... there are a lot of people who just have the worst luck). I would say that in your first 3 years you would be fairly likely to get a tour, and more likely if you do 6 years (the first 6 months or so of your career are training, and that excludes you from tours, and if you miss out on the "work up" (pre-deployment training), forget going. Then, you can't go on tour if your contract is about to expire (ie. they won't send you on a 6 month mission if your contract runs out in 3 months). With the way Afghanistan is going, I would say that you are fairly likely to go at some point in your career, but who knows.
Good luck with your training, and here are a few pointers once you get to the Regiment: someone will no doubt send you on a fools errand for one of the following: a box of grid squares, a roll of contour line, 6 inches of Fallopian tube (usually from a female Supply Tech), a tube of elbow grease, a can of radio frequencies, left hand thread pre-torqued road wheel nuts, and the two classics, checking the tire pressure on a Leopard (or tracked vehicle road wheel) and the infamous Sky Hook. My advice: smile, go about looking for said item (for about 10 - 15 minutes), return with a frustrated look, and presto! you are now a crewman (or look like a bit of a loser...... same thing, usually ;D). The other pointer is to bone up on Regimental history when you get the chance, as the current RSM is a big history guy (and a big guy), and likes to spring questions on the unsuspecting soldier.
Al
