common-law spouse of international student

[rokwo]

My boyfriend will be attending school in Vancouver for 1 year. As he is American, he can obtain his study permit at the border, correct?
I plan to accompany him for the year as his common-law spouse. Do I enter as a visitor or temporary resident (or are they the same thing?) I assume we apply in advance (outside Canada) for common-law status. How long does the process take?

I am a British/American dual citizen. Is one better to use when applying?

Thanks,
Rosanna