The big postings for Artillery are; 1RCHA in Shilo, MB, 2RCHA in Petawawa, ON, 5RALC in Valcartier, QC, and the RCA School in Gagetown, NB. There's also 4AD Regt in Gagetown, NB and Moncton, NB, but that's all Air Defence.
Outside of those, for the western area, you can also get posted to CFB Suffield and CFB Wainwright, but those seem to be base duties and not regular Arty gigs.
I'm speaking for members of 1RCHA here, and not the other Regt's (as I don't know how fast they move members). When I was posted back to the Regt back in '10, we were just reforming into 2 gun batteries, an STA battery and a FOO battery. My option to get into the STA came during a field ex when they asked who wanted to do it...
After my the first group was asked, most of our new members have just been tasked to C Bty (STA) from their posting, I'd assume it's similar with Z Bty (FOO). There have been a few members that have asked to come to C Bty, but they're usually hooked Gunners and Bombers. Once they do make it to the battery, they're loaded onto the appropriate courses as they come up.