The EU PlayStation blog
has news that PlayStation Plus members will get exclusive access to the Upcoming Resistance 3 Multiplayer Demo.
In the US, this offer is only available to purchasers of SOCOM 4 Special Editions which go on sale on April the 19th.
As to the hows and the whens - well this information will be revealed at a later date.
Resistance 3 is due to release later this year.