The only reference to the show that I found on the OC Register's site (a pathetic source for news on the whole) is a review by a clearly delusional critic who thinks the show has slipped this season. Obviously, he doesn't know what he's talking about.
I highly doubt the show has been canceled and if it had been, I'm sure it would be all over the news. Since this is AMC's first big hit and it's getting so much critical attention, they'd be complete fools to cancel it. The only reason I could even imagine that would cause them to even consider it is production costs. I'm sure it costs nowhere as much as Rome did and that show was canceled for cost - it was the most expensive show on TV at the time.