Hi, I'm 16 years old and am planning on taking a trip on either Amtrak
or Greyhound with three of my friends. Our plan is to end up in
Vancouver but were wondering weather or not the three of us will be
able to cross the border if we are not with any one over the age of
18. We all have passports and could get signed letters from our
parents if that is any help.

Hi jonah1111-ga,

The Canadian government does not stipulate a minimum age for crossing the border.  

http://www.cbsa-asfc.gc.ca/E/pub/cp/rc4161/rc4161-e.html#P135_3351

It can't hurt to have letters from your parents to the effect that in
case of emergency they are prepared to come to your aid.

To be extra sure, I recommend that you contact the Canadian consular
office in the largest city near your home.

You can get the address and phone number at the following website:

http://www.voyage.gc.ca/main/foreign/fordest/foreign_view_client-en.asp

I hope this does the trick.  Have a great trip.

Alanna-ga

That was perfect, thank you so much.

From this site
http://travel.state.gov/travel/tips/regional/regional_1170.html
it states that "Any person under the age of 18 and traveling alone
should carry a letter from his/her parent or guardian authorizing the
trip. Travelers without such documentation may experience delays at
the port of entry." Hope this helps.

Search topics: US canadian border age
Search engine: ://www.google.com.au

It wouldn't hurt to get it notarized.