I don't know about Canadian schools, but if you identify as AI/FN, you can certainly apply to US schools as AI/FN. Most applications will ask your tribe/nation (I assume you know that) and some, your enrollment status. For those that ask enrollment status, you should write a short addendum and explain your situation. Most law school understand that status in North America is very complicated - being honest and upfront is the best policy.
If you belong to a Jay Treaty tribe, you may be able to get a US CDIB card, with proper documentation. It won't help or hurt your application, but may help you in other situations, should you attend a US law school and remain in the US.