Blockbusters and tax credits started the trend, but green-screen filming sure accelerated it. Now that so many movies are almost entirely CG, it really doesn't matter where the green screen studio physically exists.

The silver lining (for Americans) is that Hollywood movies are still very Hollywood. Canadian actors, Canadian crews, and Canadian filming facilities all combine to make utterly American films. If real locations are used, they're carefully chosen so that Vancouver stands in for New York, Calgary for Minnesota, etc.. Canadian references, accents, and values are all carefully erased.

The one thing that seems to stay stubbornly American is the money people.