To add my piece of the puzzle, I am an arty officer, 14 years in. Every trade as its pros and cons. Looks like the arty is slow to promote, both for Officers and NCOs, compare to Inf and Arty. We did had a few years in a row with 0 promotions in quite a number of rank levels. Because of this fact, a good number of excellent captains transfered trade (Int, Pilot, Eng, PA, all friends of mine) some of them are majors now, and they would probably still be captain have they decided to stay. The fact that we are 40 captains short is probably directly linked to it.
As far as the job is concerned, as an arty officer, most of the time, you do the same thing as any other cbt arms officer ... paperwork, staff work, etc. Only on exercise or on operation do you do the job for which you are trained for. The best one I had as arty was as a Observer (FOO). You are then totally away from your arty unit and under op control of an inf unit, armour unit, or combat team. You are then as forward as they are. The FOO must be able (as the engineer officer) to advise his supported arm commander (usually of the rank of major for a FOO) on all indirect fire usage, including the use of tanks in the fire base role. The arty officer must acquire early in his career deep knowledge of tactics of all arms in order to understand two levels up the tactical situation (this means that you have to be able, if working at a cbt team level, to have the tactical vision of the battle group, and to understand the objective of the divisional artillery).
By the way, the myth that the arty is far behind is false. For guns with an 18km range, two thirds of the range must be pass the front line, leaving the guns 6km from the fight, with recce officers being very close of enemy areas if on the advance.
As a FOO, you attend to Battle Group commander's Order Group with the major you are supporting. That is were you meet with your own arty Major (bty commander), which then gives you supplementary instructions on arty matters and tactics.
If you are also trained as a FAC (Fast Air Controller) you could be given the task of directing a F-18 onto a ground target, since this is also an indirect fire capability.
You and your team act just like infantry while performing any other non arty related tasks. You must then be able to lead a platoon if needed. You also are capable of setting up local defense and direct fire assets for an infantry company, because of your training and knowledge of tactics.
The soldiers you comand are very technically capable. You or your men are often asked to help with communication issues while with infantry, since an gunner is normally very efficient technically in this field, when sigs are not around.
On most UN and NATO missions, you would deploy in an infantry role, except when deploying guns or mortars.
In summary, an arty officer must be a decent infantry officer on top of being an arty officer. But don't count of doing arty stuff all your career. I would say that 80 % of the work you would do in a 20 yrs career would be spent doing mostly staff work, and for the 20 % on arty duties, I am being very generous.
There are experienced arty officers in Kingston and at RMC, talk to them to make up your mind. Good Luck ! UBIQUE
Like some other people have said, you should ask your friends that already attended training at the Arty School. After CAP, Phase 3 or Dp something or another is a combination of field, air defence, and locating modules. The bulk of the work focuses on the field side of the house. I hope this helps out!! P. S. Don't believe everything you hear because all three have different things to offer. Most RMC cadets end up on the field side. 
