Hi,
I paid my RPRF online and sent the receipt filled with my application data (Applicant name, UCI...) by regular mail and also by email. As far as I know RPRF can also by paid in a BFI branch. Regarding medicals, in Cuba they are picked up in the hospital by the Canadian Embassy and sent afterwards to MCVO, so after doing the exams you just have to wait until MCVO receives them. When you finish the exams they will give a receipt but you don't have to send it to MCVO, at least I didn't in my case, I just sent an email stating that I have undergone my Medicals as requested.