The big difference comes down to this: Paramedics/RPNs study through a college, while RNs, study at a university (or collaborative program, ultimately leading, still, to a degree).
So in Canada, you can't bridge these two programs/professions yet, but what you can do is if:
1) You took your highschool courses as "University" Level courses, apply to the RN program, but you still have to do four years.
2) You took your highschool courses as "College" Level courses, you can finish the paramedic program, do the RPN (college) program, then bridge after that to the RN program (they have RPN to RN bridging programs, cumulatively 5 years- 2 in college, and three in university). Kind of cool you'd have three licenses..
The reason why most BScN programs will not allow you to do the program in less than four years (regardless of degrees/diplomas) is because there are clinicals each semester that you must finish. These are not offered in the summer, and so, the student that fails clinical in second semester of first year must then wait the following year, to re-do their clinical in second semester.