Alberta would need the consent of the councils for Treaty 4, 6, 7 and 8 in order to take their land with them. The treaties are between various First Nations and the Crown of Canada and are not transferable to an independent Alberta without consent.
Some provinces have non-treaty land, acquired through land purchases or conquest. Quebec, for example, had the right to take roughly the southern third of its territory when it discussed separatism. But that's not the case with Alberta — it is entirely composed of treaty land.
This means that Canada cannot grant them independence, even if it were to accept the results of a referendum that meets Clarity Act requirements. That alone makes Alberta separatism a non-starter. There's no legal route for Alberta to separate from Canada without negotiating new treaties with the treaty councils in order to get their consent, and they've already signalled they are not willing to do so.