An independent Alberta would keep its place in NATO and continental defence.
Stated by: Implied by some Alberta independence proposals
Summary
Membership in alliances follows the country, not the province, so a new Alberta state would not inherit Canada's seat. NATO accession under Article 10 requires a unanimous invitation from every member and, on its face, is limited to European states, which would make Alberta's path especially difficult. Joining would take years, during which Alberta would sit outside Article 5 protection. Presenting continued membership as automatic is not accurate.
Evidence
Article 10 of the North Atlantic Treaty allows accession only by unanimous agreement of all members and refers to inviting any other European state.
NATO (North Atlantic Treaty, official text) (opens in a new tab)
NATO enlargement requires ratification by all current members, and Article 10 limits eligibility to European states, complicating any non-European applicant.
A defence analysis notes Alberta would lose NATO Article 5 protection on separation and that any application would take years to process.
New Peril (APP, NATO and the cost of defence) (opens in a new tab)