Ireland's shock win was the Black Ferns' first loss at a World Cup since 1991, where they were beaten at the semi-final stages.
The Red Rose ladies were runners-up of the last three tournaments, losing to New Zealand on each occasion, but Mclean now believes they may have the edge.
She told BBC Newcastle: "Ireland beating New Zealand is massive for us.
"Since 2010, we've played them nine times and they don't have that hold they used to have.
"It'll make a massive difference if and when we play them, we just need to worry about Canada first."
England have made a solid start to the World Cup in France, with comfortable victories over Samoa and Spain, but they face a tricky test against Canada on Sunday, knowing a win will guarantee a semi-final spot.
Mclean added: "Undoubtedly, all the games we've ever played against Canada have been tough, physical, quick tests.
"We are lucky our coaches and analysis teams do a lot of work on the details like scrums and line-outs.
"It's easy for us to go in and pick up on things."
However, England have been rocked by the news that wing Lydia Thompson has been forced out of the tournament with a groin injury.
She has been replaced in the squad by Natasha Brennan, who has also represented her country at hockey.
Coach Gary Street said: "This is unfortunate for Lydia. But it is fantastic to call up Natasha. She missed out by the narrowest of margins."