Originally Posted by
RooseveltL
The app is very liberal with nearby airports during irrop. Once you get the red ! - it allows you to rebook typically within 250 miles whether same day or future days if seat are available.
UA Reservations had told me that once expected delay is >2 hours any airport within 300 miles of the original is fair game; obviously preferably online (e.g. UA/UA express operated) but not required as long as UA has an interline agreement. Of course the app never offers offline options.
E.g. earlier this year ORD-CLE UA (Club) was offering TOL on AA, PIT on UA/AA, DTW on DL, and I want to say a Canadian port snuck in there as well (YYZ?)... But in the end based on weather and timing I just picked up a one-way rental.
To the OPs question as long as you can legally enter the country I don't think it matters to UA where you're going once the invol tag gets applied. Pretty sure one of the times I was near the southern border they offered an airport in Mexico ... If it weren't for the logistics of getting from there to where I needed to be it would have been an appealing option (schedule, etc.) too.