The winger, 23, set up Martin Samuelsen's goal before scoring the second in Saturday's 2-0 win over Charlton Athletic at the Abax Stadium.
Maddison has now provided a league-high 15 assists for 11th-placed Posh, who are eight points off the play-offs.
"On his day he is one of the best in this league, if not the best," McCann told BBC Radio Cambridgeshire.
"We want to try to get his best out of him more than not his best, if you know what I mean. He's bringing a lot more to the table this year."
Peterborough signed Maddison, who started his career at Newcastle United, from Gateshead in 2014.
"Goal-scoring wise I've been a bit off," said Maddison, who has scored eight times this season. "But assist wise, I'm up there. I've just got to help the team in any way I can."
Peterborough United manager Grant McCann says Marcus Maddison is the best player in League One "on his day".