Do you need permission or a note from your parents to go to Canada even though you have a passport and your under the age of 18?

Yes you do. upon entering the country, they will ask for some type of proof that you are actually visiting family or friends(such as a letter or invitation). coming back to the USA, they will not let you pass security if you dont have a note stating that your parents know that where you are and when your coming back. however, they do not check this when you are entering the country. and yes, you will need proof even if you are traveling with an older sibling