Your first posting, in any trade, is usually more dependant on your element than your trade really.
Air Log goes to Wings, Army Log, to Army Bases...you get the idea.
For subsequent postings, you usually do not go anywhere until you have done a few postings as a Capt. Then, in the support trades, it can be more open. It comes down to a game of probabilities really. Most Army Log types below Maj are in the support bases and field units. After that, most are in command positions (Kingston, Winnipeg, Halifax/Esquimalt, Ottawa, even Borden). Most Navy Log stay on the coasts or Ottawa (or Quebec, NavRes HQ). Air Log are the same as their Army compadres.
If you go Int, that's a bit different in that the largest concentration of Int dudes and dudettes are in Ottawa, so, your chance of a posting there, at any time in your career, is larger. There are fewer operational type postings for Int at all rank levels and most stayed based out of the Ottawa area.
When I left RMC in '08, I was given the choice of any posting in Canada.....as long as my choices were Edmonton, Pet or Gagetown ;D. I have been told that I will be remaining in my current area for another 2 postings, possibly more, depending on my standings on the merit list once I hit EPZ.
Wook