>The Indian reservations belong to the US.
Notice how carefully I worded my comment:
>70% of the land is not the U.S. Government's to give.
"The federal Indian trust responsibility is [...] a legally enforceable fiduciary obligation on the part of the United States to protect tribal treaty rights, lands, assets, and resources." [0]
The questions of armies and building bases I'm not sure have been raised, so the legal precedents might not exist. Sufficed to say, however, that the GP's hypothetical sale to Canada would be wholly infeasible in light of the treaties between the sovereign tribes and the US, as well as the legal complexities those entail.