Derek McGrath, a prolific Canadian actor, voice actor, song writer etc., is the voice of Chief Quimby in the new series. Quoting a July 9 article from My Kawartha:
Mr. McGrath has been acting for almost 50 years - on stage, on the radio, on television and in the movies - and has written more than 100 songs. He has worked with everyone from Jack Lemmon to Billy Ray Cyrus. More recently, he provided a voice over for Mike Crosmaz’s independent zombie film, Walk With Me, and just wrapped up work as Chief Quimby on the reboot of the Inspector Gadget cartoon.
You can read more about McGrath's long and productive career by clicking this link. Here, however, I'd like to focus (naturally) on the Gadget-related aspects. Firstly, regarding the production timeline of the new series, the above statement tells us that voice recording has finished - definitely for McGrath's work as Quimby, and likely for the entire cast. This, in effect, should mean that all the episodes for the new show have both been written and voice-recorded by this point. And of course, we already know that the show is well into animation.
But back to Quimby's voice. Personally, I really hope Mr. McGrath can portray Quimby with the same charm and personality that the character had back in season 1 of the original series, as played by another Canadian, Dan Hennessey. (Admittedly, that also has a lot to do with how Quimby was written: In the original season 1, I think, despite his occacional frustrations with Gadget, he was portrayed as a more charming and sympathetic straight man than in any later versions.) I'm not familiar with McGrath's work and really have no clear expectations of how he will sound as Quimby... but here's a rather charming video interview from last year which lets us hear his natural voice: