I think the US government and a lot of big websites have a pretty good relationship like (tax breaks) with each other, so it is unlikely they will move to Canada or some other place, and the lost of US jobs might be bad for the economy.
But, I do believe most big websites have a office or building in Canada, and most countries, so they can hire talented people without them requiring to move to a different country, and for the website to have a presence in other countries.
it would depend if the country they are moving to would benefit the move. but I hope not, we can't lose anymore jobs. Unless it moves to japan, I will follow them if they do
Maybe some of these companies I mentioned will open more offices in Canada, and other countries to hire a lot more talented web programmers, marketers, engineers and designers without them requiring to move to the US.
Yahoo and Google already has a few offices in Canada.