You need a job offer and can't start working for the company in the US until you have obtained work authorization. Often the best option for Canadians is the TN

You need a job offer and can't start working for the company in the US until you have obtained work authorization. Often the best option for Canadians is the TN and broadly there are two paths, applying in advance with USCIS and then raveling to this with this approval notice or applying as you are traveling to the US with CBP at a Canadian airport, at the US-Canada or US-Mexico border, at a CBP office at US airport if traveling to the US from a country other than Canada.