"XL / extra large" is a 'Series 500' kennel. Those, when assembled, are not accepted for transport on any type of RJ. CRJs and ERJs accept 400-size kennels at most. When disassembled and the halves stacked together, they fit through the cargo door but I don't know if AA will accept them, or, for that matter, decides to treat them as regular baggage and charge you the $150 oversize fee - I think the resulting package (especially when you have a few of them stacked together) will exceed the 62 linear inches baggage limit....
AA lists the cargo specs on aa.com:
http://www.aa.com/i18n/aboutUs/ourPlanes/crj700.jsp.
Measure out the whole package and write to AA.
And adamki has a valid point: When I brought my dog from Spain, I purchased a kennel online (
link) and had it delivered to the shelter I picked her up from.