if i want travel from US to Canada by bus, how can i do?

which bus company? and where can i buy the tickets?

Buy a ticket, take the bus. Have a certified copy of your birth certificate and a picture I.D. with you.

Greyhound offers service on the east coast to Montreal, Ottawa, and Toronto form cities like New York, Boston, and Providence. I would think they have buses that can cross into Canada at other points too.

Coming by bus, you will need a passport, or a birth certificate and at least one piece of photo ID.

Try GREY HOUND and Coach Canada

http://www.greyhound.ca/
http://www.greyhound.com/

Greyhound company. But if you're coming from Buffalo, or New York city, maybe you can check into http://www.coachcanada.com/ .