The great fear of many Canadians, especially the politicians, is that Canada will one day be "enveloped" by the UnitedStates and become the "51st state." 
''or, that this has already happened.''

Canada is a nation that has had to fight to justify it's own existence for almost 100 years. For many years, Canada's status as a virtual colony of Britain made her sovereignty from the United States easier to justify. However, as the British links have eroded, justifying Canada's status as a sovereign nation that is already culturally identical and fully economically tied to the United States becomes much more difficult. 

''If you think that Canada is culturally identical to the USA, you haven't lived in both places, or you haven't paid attention when you did. Economics is stickier.''
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Wow, never heard of this before... How are the Canadian politicians envisioning this would happen? US takeover? - I can't foresee that. Grassroots movement in Canada to ask the US to take it on as a state? In any case, I can't imagine the US ''wanting'' one huge additional state, although I don't [?] the respective populations as that would effect the number of representatives it would have in the U.S. House of Representatives as compared to other states.
''The US is a corporate government. After those US corporations assume a controlling interest of Canadian assets, Canada becomes a de facto part of the US''

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Hmm, interesting. Forgive me for being Belgian, but seen from a far, this is what I know and think. (1) Canada is member of the Commonwealth, right? This is a left-over from the 'British links [that] have eroded' as far as I know, doesn't yield much, but still is something the US doesn't have. The Queen is watching over you, in the USA, ''no-one'' is looking over the President. (Correct me if I'm wrong, by another perspective, this is where 'corporatocracy' might come in.)
(2) What about Quebec? It's dominant language is French, right? And as most territorial and language bound minorities, there is a movement that pushes independence. Happily for Canada bilinguality goes quite peacefully, and independence of Quebec is not that hot of an issue (as far as I know, correct me if I'm wrong). By comparison in Belgium (extreme) right-wing politics is on the rise, not good in combination with French-speaking - Dutch-speaking tensions.
(3) So, I can understand that a neighbouring country like the USA keeps coming back in political comparisons, much like The Netherlands and other European countries here in Belgium politics, but in the end the right decision in the importance to the country must be taken, not the one that takes you closer to the USA. Which forms a good basis to evaluate politicians by.
(4) In any case two governments decide to coincide, one or both sides needs to change a great deal. Since this is a discussion about Canada State, and not the USA becoming a Canadian Territory (hmm), it would be Canada losing quite a bit more than it's current structure in economics and healthcare (to just name 2). (conclusion) Summing up these few things, I suppose there are enough grounds to stick to Canada as a separate nation.

-- StijnSanders