I lost interest in WoW awhile back, but depending on how good GW2 is I might cancel my SWTOR account. Basically, if GW2 does the things I enjoy (PvP) better than what I'm currently playing, then it would be silly to continue with the latter.
That being said, I know most all of the Cupcakers are big Raiders, so I doubt GW2 will scratch that particular itch well. But its really easy to justify playing both since only 1 has a monthly fee.