Which large body of water forms Canada's western border and is important for trade with Asia?

A. Pacific Ocean
B. Atlantic Ocean
C.Great Lakes
D.St. Lawrence River

Reward for answering correcty: Brainlyiest & 15 points
Note:Please keep your answer simple and understandable) A,B,C,or D is all I need as an answer not a whole bunch of paragraphs.Thank you :)