Canadians can stay up to six months from the entry date before you need to leave the US and re-enter. If you want to stay longer you can request an extension, from the Visa Waiver Program [official page][1]:

 > If you are from Canada, the length of stay for tourism is up to 6 months. Canadians may file for an extension of stay with the U.S. Citizenship and Immigration Services.

  [1]:https://help.cbp.gov/app/answers/detail/a_id/194/kw/