Only reason I would say get rid of the pacu is that they sometimes like to nibble or take a nice bite out of their tankmates. I just wouldnt want a beautiful pair of aro's to get messed up by a pacu.
If you have a Big AL's around you they can sometimes order you a custom tank of your dimensions but they are not cheap. Your best bet would be to find a local tank builder. Try to find fish clubs in your area or Canadian web forums and ask about builders in Ottawa. If you are willing to drive to T.O. or Barrie I could give some names and numbers.