Unfortuntely, a PC PREL (Project file) will not open on a Mac, and vice versa.
Now, a PREL will often Open in PrPro version that is contemporary with the PrE version - with certain limitations. If you have a recent PrE version, a recent PrPro version, and a simple PrE Project, you might be able to Open those, across the two programs.
As far as being X-platform with PrPro, I have never read of anyone testing that. If it works, please report.