Normally a permanent establishment under a treaty follows a fairly standard description and needs some sort of office, site, mine, etc.
However, the Canada-US tax treaty adds some specific situations.
If you are an individual, you will have a permanent establishment in the other country if
1. services are performed by an individual who is present int he other country for an aggregate of 183 days or more during any 12 month period, and
2. more than 50% of the gross active business revenues during that period are as a result of those services.
If you are doing business through a company or other enterprise the rules are slightly different. You will have a permanent establishment if
1. services are provided in the other country for 183 days or more in any 12 month period with respect to the same or connect projects
2. those services are provided to residents or permanents establishments in that other country.
One of the differences between these two calculations is the the calculation of 183 days - for an individual it is the number days present but for a company it is the number of days worked. For a company, many individuals working on the same day will only count only as one day.
