As per census.gov there are approximately 27 million businesses in the US in 2008. However, more than 21 million forms are non-employer firms. Approximately 6 million firms are employer firms. Of these only 18 firms have more than 500 employees, which is negligible. So we can conclude there are 6 million businesses with 1 to 499 employees and 2.5 million businesses with 5 to 499 employees in the US.
As per statscan, in December 2012, Canada had 1.2 million small businesses with 1 to 499 employees on payroll. Similar to the US, approximately 50% of the workforce is employed by small business. Canada is approximately 10% of US population, so one would expect Canada to have 600 thousand small businesses. With 1.2 million small employer firms, Canada may be twice as entrepreneurial as the US. That said this analysis is purely qualitative and does not take into account the quality and size of the average business. The results are also surprising given the fact that US leads Canada significantly in the ease of doing business report compiled by the World Bank.