Canadian going to the USA

Hello, I have a question: besides having to present the Canadian passport at the border to be able to enter in the USA I would like to know if I need any proof that I will be going back to Canada ( Like an air ticket).
I intend to go to California next month and will spend a few months with my boyfriend there.
Can someone asnwer me so I can buy my ticket back to Canada in advance.
p.s: I will be arriving to USA from Brazil.
Thanks.

How long is "a few months"? Yes, you will need proof of ties to Canada, like a return ticket, a permanent address, a job, bills etc etc etc.You may or may not be denied entry if you tell them you're there for "a few months to visit my boyfriend".