Some already have 81's, but there are not many left (80ish including log stock), so not many to go around for both Reg F and P res to begin with, and I doubt it would solve the problem even if there were.
A misconception I've often heard is a mortar is an indirect fire weapon just like a howitzer, so the training is equivalent, it is not. I've recently seen the difficulties my own unit had when we went back to guns after doing only 81 training for about a year.
P Res Artillery units are expected to force generate individual Tps for Reg F Artillery units, and it is quite a stretch to go to towed artillery if you're only trained on a mortar. The M777 is comparatively very complex, but at least having some basic understanding of the nature of towed gun deployments is a much better start pt, than working with mortars that can deploy just about anywhere.
We've already received the message from the Tech authority confirming what Craig B has said about the C3 going, he is also correct we do not have working gun line comm's and are regularly short vehicles; redistributing mortars about the P res will not solve those capability/training deficiencies
I support what Petard said about the 81mm. If a soldier was trained on a gun, it is a relatively short process to convert to a medium mortar. However, if the same soldier had been trained on a mortar, to convert to even the C3 is a difficult proposition. Let me illustrate the former. In June 1974 I was posted to the Artillery School as CIG. (In those days the chain in the school went Commandant, CIG and the training wings, gun park etc.) A few weeks after I arrived, there was a coup in Cyprus which led to the Turkish invasion. The Canadian contingent at that time was based on half the Airborne Regiment, and there had been some spectacular shots on TV of them rescuing people trapped by the fighting. Anyway, the Commander FMC was coming for a quick visit. That morning one of his staff took me aside to tell me Cabinet was expected to approve the deployment of the rest of the regiment to Cyprus that day. This would include the airborne battery which was saddly understrength, mainly because the gunners had not been recruiting anglo gunners for several years.
We had only the second anglo TQ3 troop since 1969 or 1970 in house and it had about two weeks to go. The kids had all qualified on the C1 and the M109 and were doing the same on the L5. About half the course had volunteered for the airborne battery, so that was a step forward. I grabbed the troop officer and an AIG who had just reported in from the battery and told them what was up. I then told them to start training the troop on the 81mm just in case. The commandant was away, so it fell to me to meet the Commander FMC when he arrived. I made a point of mentioning the TQ 3 troop and that on pure speculation based on reading the tea leaves, we had started 81mm training as a contingency. He looked at me for what seemed like a very long time and then said something like "Send them to the Airborne as soon as you can." They left in about four or five days, after qualifying as mortar numbers and were off to Cyprus soon after. They all did well with the battery and most became long time airborne gunners.
Having gone through the RCA Depot years before and being trained as a gun number on the C1, I don't think we could have done it if they had not been trained on a gun before, and they could not have converted from mortars to guns in the same time.