Artistes and athletes are a special bunch of people for tax treaty purposes. Look for a treaty article to override business and employment income to ensure that where the artiste or athlete is performing the source country may tax the income.
This is regardless of whether or not the artiste or athlete has a permanent establishment.
In the Canada-US tax treaty, there is a provision to exempt income where the gross receipts are less than $15,000 (note that is gross receipts, not net).
There may be special rules for teams – such as hockey and baseball teams who regularly play in both Canada and the US – those are taxed under other articles.
Whether a speaker is an entertainer or involved in business can be tricky. For instance, if Al Gore comes to give a speech on conservation – would you classify him as an entertainer or a business person?