Final answer:
The Columbia River starts in Canada and flows through the northwestern United States before reaching the Pacific Ocean.
Step-by-step explanation:
The river that starts in Canada and flows through the northwestern United States before reaching the Pacific Ocean is the Columbia River. The Columbia River is one of the longest rivers in North America, spanning approximately 1,243 miles. It originates in British Columbia, Canada and flows through the states of Washington and Oregon before emptying into the Pacific Ocean in Oregon. The river is known for its scenic beauty and plays an important role in the region's economy.
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