Both are just toys. The MPX will be long forgotten before the ps90. The draw backs and uniqueness of the ps90 are what make people want it. The MPX is just another over priced 9mm ar15 style pcc.
The only advantage PS90 has over anything else is 50rd mags and suppressor ergonomics. Which is maybe relevant for special forces, but both are irrelevant for Canada's civ market.
P.S. If you look at military adoptions, many militaries think that switching from 9x19 to 5.7x28 is not worth the logistics trouble. FN had both pistol and smg ready to go for US army and Army picked P320 and APC9.