I'm gonna probably go against the grain and say it would be ideal if you could get stuck somewhere that seems completely not job-related, perhaps within your element. I'm biased towards finance* of course, but literally anything that will let you see some aspect of the RCAF that you won't get to see/interact with once you are trade-qualified. Putting someone who's going to get lots of experience on the operations side of the house might prepare them better for their first job, it offers not a lot of extra in the long view of things.
What's the difference between 4 years of OFP experience or 4 years of OFP ops experience + 2 summers of OJT ops experience? Probably not much...... how about 4 years of OFP experience vs 4 years of OFP experience + 2 summers in a Wing Comptroller office, or a Base Tn office, or a Base Supply office? I'd think the latter is going be better as they take on more responsibility and find themselves having to make plans that consider finance, or transport, or supply, or all three. The higher up you go, the more of a "generalist" you have to be. So I think what we do with OJTs is a wasted opportunity, they'll never get another chance to learn the other side, they'll have all kinds of time to learn their own realm.
For a pilot, I don't know what that would be, I don't know jack about the RCAF, but if I had to point in a general direction, helping out in any of the Base logistical services such as transport, maintenance, finance, supply, human resources, etc. would probably be a good place to start. Far too many on the Ops side that are oblivious to their logistical chain (and vice versa, far too many Log types that are oblivious to operations).
Being the person that has a schmick of a clue about the other side can, in the future, easily make you the person at the table that seems to always come up with the best/easiest solutions to what many people thought was a complex problem.
*While no one gets any real finance experience and the DLN courses you get are absolute shyte, everyone ends up getting affected by it whether they are given financial authorities or not. And someone who understands what's going on behind the curtains of their budget can do a lot of good for their mission and the people that they are leading. And then when you become a CO or Ops staff officer, you're able to solve problems that align with your goals and not be spoon-fed a suboptimal solution from someone who doesn't understand your problems.