Promoted from Sky Bet League Two last season, the Us have adapted brilliantly to life in the third tier and after two wins in a row this week they are sitting very pretty in 10th place.
They will rightly arrive at Sixfields on Saturday as the favourites to progress, but Bonner is says he is wary of what Jon Brady's team is capable of.
The two teams met in pre-season, drawing 0-0 at the Abbey Stadium, and the Cambridge boss knows his team are going to be tested this weekend against a Town team on a four-match winning streak in league two.
“We have to go and be ready to play against a really in-form team," Bonner told cambridge-united.co.uk
"We played them in pre-season, so we have a bit of knowledge of Northampton and now we have to go into the game and try and back up what has been a really good week for ourselves so far.
“They are a team that are really hard to create chances against, they have had very few chances conceded in the last four games and in the wins, they have had lots of clean sheets.
"There is a physicality about them, as well as a directness to their play.
"They share some similarities with us I think last year, and we know that they have some good players in there; some of them we know well.
“The game is just up the road and we will have maybe near on 1000 supporters at the game, so we want to try and create an atmosphere in the away end with our performance and ultimately then progress ourselves through to the next round.
"It is a game that is worth looking forward to, and sometimes when you break from the League routine it can be a good thing.
"In the end it is about momentum and trying to keep on a winning run if we can."
Former Cobblers defender Lloyd Jones has been a key man for the Us so far this season, but he will not be involved against his former team-mates on Saturday as he is injured.