But the midfielder refuses to count the Pilgrims out of a promotion push.
McGuire is reunited with Boston manager Adam Murray and this pair played in the Conference together as team mates in the Stags midfield.
Birkenhead-born McGuire also played under his new boss when he was in charge of the League Two club last year.
They now themselves back in tandem after a loan deal was agreed with Mansfield for the experienced player.
McGuire said: "The hopes for season being realistic are a push for those play offs in very tough league.
"There are some big teams with great resources and the National League North is toughest it has been in years.
"Hopefully we will be the surprise package of the league. I don't see why we can't be really competitive."
Maguire is one of 12 new signings. The manager opted to clear the decks for a fresh start and the 33 year old campaigner likes what he sees so far.
"All of the new players have settled in well, me being one off them. You can see we are working hard on training ground ready for new season made some good signing and were gelling well," said McGuire.
"I know what this league's about going up with Fleetwood, and so do the players because most of them have played here before. So it's a big season for us.
"This league is the most competitive there is and all the players want to play in it. I think we can be up there - everyone is so motivated to do well."