Re: Chicago to Grand Canyon
Good Sam's web site has a pretty good route program.
Note that 2 weeks for that trip is cutting it pretty fine. I regularly go between central IL and Tucson, AZ and I suspect it will take you 4 full days each way (or 3 very long days). 8 days out of 14 leaves only 6 for sightseeing.
The way I usually go is over to St. Louis, then down I44 to Oklahoma City, then I40 to the Grand Canyon area. With a trailer (to avoid the high, per axel toll, in OK) we went over to Kansas and then down I35 to OK city. A couple of places of interest off I40 in NM and AZ are the Petroglyph Natl Monument and the Meteor Crater. In the Texas panhandle, there is a smaller version of the Grand Canyon (Palo Duro Canyon); the best thing about it is you can drive down into it rather than riding mules as in the Grand Canyon.
In my opinion, the best way to see the (south rim) of the Grand Canyon is Marvelous Marv's tour. There is a nice RV park right off the interstate about 30 miles west of Flagstaff (Canyon Gateway Park perhaps). They are Passport America members so are cheap, and if you book the tour through them, there is a significant discout. Marv picks you up and busses you to the Canyon, shows you all the good stuff, gives lots of info, lets you eat and shop, and most importantly, avoid the crowds and the hassles of trying to see it on your own.