Canberra-product Monaghan played two games for the Blues in 2008-2010.
NSW have won just one of the past 10 Origin series and are coming off an embarassing defeat in Game III last year.
“It’s gotta be New South Wales mate,” Monaghan told Love Rugby League.
“It’s a young side but it can do the job, fingers crossed.”
Monaghan featured in Castleford’s fine 34-14 win over Warrington at Magic Weekend in Newcastle on Saturday.
Cas turned round a 14-0 deficit to score 34 unanswered points to beat the Wolves, and Monaghan was delighted with the result against his old club.
“After the way they turned us over earlier in the year it was good to get one back on the big occasion,” he said.
“Magic Weekend is a magnificent occasion and the boys have built up a bit of momentum there, so hopefully we can build on that.
“We gave them too much early on, they were good to start, but to come back and turn the game round was unreal.
“They played well, but we just gave them too much ball and let them roll through us early.”
Monaghan is also excited by the quality of the Castleford squad around him.
“The quality of the squad across the board that we have is unbelievable – it’s skilful, big and athletic,” he said.
“This is only the start of something I think, and hopefully we can stay injury free.”
One player in particular who has impressed Monaghan is winger Denny Solomona, who bagged a brace of tries in Newcastle.
“Any 50-50 ball, if it’s in the air, or going in or out, he’s going to finish it,” he said.
“That’s the sign of a quality winger and he’s up there with the best I’ve seen.”
Monaghan is happy at Cas, and can’t see hmself leaving at any time soon.
“I’ve got another year at Castleford, and I’ve really enjoyed the move,” said the former Warrington winger.
“It’s a very easy club to fit into – a great place to play rugby and a great place to live.”