Wow, a 40 minute layover is not very long. Plus, it looks like you have an XJ plane from Marquette to Detroit, and those usually land at Terminal C, and your DTW to Orlando flight will leave from Terminal A. Not a terrible hike, but at least 10 minutes, depending on your gate -- and your bags will have to make the trip, too.
That said, Northwest is offering the flight, so they think you'll make it.
I am going to tell you not to worry, because you and your bags will get to Orlando. But you may want to call Northwest and see if they can (for free) put you on flight 3196 (MQT to DTW, arrives 12:55 at DTW) and then flight 422 from DTW to MCO (leaves DTW at 3:10 pm, arrives MCO at 5:41 pm). That would give you a 2hr15min layover and put you in Orlando about 1.5 hours after the original trip. Worth a shot. If they won't do it, then maybe you can post about what to do if you have a short layover.
FWIW, I believe NW flies direct to Orlando out of Minneapolis (MSP), Detroit (DTW), Memphis (MEM), Indianapolis (IND), and seasonally out of Flint (FNT), I think. Also, keep in mind that by January Northwest and Delta will have merged. From Marquette I don't think that would affect your flight schedule (DON"T let them try to route you MQT to DTW to ATL to MCO!), but just an FYI.