Do your homework about Canada. Most Americans are appallingly ignorant of Canadian history, culture and geography.
Recognize that important regional differences exist in Canada and prepare to adapt.
When in Quebec, learn a little French; Québécois greatly appreciate it when you take the effort to talk to them in their native language.
Do not compare Canada with the United States.
Do not use the term "Native Americans" to refer to indigenous peoples. Many Canadians find the term offensive. Canadians refer to members of these groups as "people of the First Nations."
Do not take sides in debates about contentious national issues (especially when they concern such issues the status of Quebec, the place of the French and English languages in Canadian society, etc.).