There are NO States the disallow a 45' coach but there may be some minor roads where a 45' coach is not allowed. However, that's OK as you should not be there anyway!
There will be some parks that don't have room but there will be one in the same general area that does. You can take a look at the places you like to travel on www.rvparky.com and look for big rig sites. Even some of the sites without that rating can still accommodate your coach, you just have to give a call first to find out.
CA is the only State with a known length restriction enforcement and that is that you RV and your toad cannot exceed 65'. Sounds like a good reason to avoid CA but it's something that can be worked around unless you plan to spend many months in CA.