While there was some interest in joining the US, the US was not that interested once Canada assured Truman that they would respect the US's basing rights. Plus it was very doubtful that it would be admitted as a state and I doubt that Newfoundland would be happy as a northern Puerto Rico. The referendum that was held also did not offer union with the UK as a choice as the UK did not want the financial burden. The "Commission of Government" option (ie colony) only got about 14% of the vote in the first referendum in any event.
How do you think it might go in this Timeline?