TD's come in waves. He will end up with about 12 (floor) to 14 (ceiling). The Packers and Bears will not allow him in the endzone. They will sellout on him. No single coverage.
Calvin scored three times in four games against the Packers and Bears last year. And neither of those defenses appears to be as dominant this year as they were last year. To answer the question, yes, I think he can break it, but I think around 17-18 is the likely end result (assuming he stays healthy).
As a comparison, when Moss set the record with 23 TD catches in 2007, he had:
-3 games with zero TD catches
-7 games with two TD catches
-1 game with more than two TD catches (when he had four against Buffalo)