Good thing is, most OT's (especially from the Cbt Arms) are some of the best MP's we have. With your qual's listed including tour, you should have no problem being able to swap over. The only thing getting in the way is the numbers game, as they're not accepting too many MP's OT side. However, if you have time to kill and are succesfully selected upon completion of MPAC, it should be nothing but playing the waiting game.
Hope you manage to score a position at an MP det, and not getting stuck at a field pl. We have a mbr getting posted into 1 MP Pl straight from QL3. Also another mbr was 12 years 3rd Bn PPCLI, MCpl, Small Arms Qualified, spent 3 years at a det in Gander, and then on posting to Edmonton... you guessed it, Field Platoon! It's really not a horrible go, sometimes it's a pretty gucci meathead field time, others it's more like Infantry Lite, and 90% of people have no idea what they're doing.
Overall Good luck!