Given that he has only vetoed two bills, and that his administration has generally been content to accept the trend towards corporatism and overall erosion of civil liberties that existed before he took office: No, I doubt he'd Veto SOPA. Similarly, I doubt that McCain would have vetoed SOPA, had he won, and I doubt that most of the current crop of Republican candidates would veto SOPA.
I do wish he would use his veto, if it, or something like it passes, but really, I hope nothing of the sort ever reaches his desk, acknowledging that my hope is very likely in vain.