Let me see if I can find your a source link.
Can PS4 and PS3 users play together online, cross-platform?
The functionality is technically possible and some developers may choose to support it for their titles.
Considering the PS3 does not have GW, and the PS4 does, I am gonna change the answer from a flat NO, to I doubt it (that is not an answer).. helpful may
As well, the PS3 doe snot require PS+
But from a COD perspective:
Answer is NO (for COD)