Final answer:
The Mackenzie River is the largest and longest river in Canada, entirely in the Northwest Territories, sourced by Great Slave Lake, and empties into the Beaufort Sea.
Step-by-step explanation:
The largest and longest river in Canada, entirely in Northwest Territories, sourced by Great Slave Lake, and emptied into the Beaufort Sea, is the Mackenzie River. The Mackenzie River is approximately 1,080 miles long and is a significant waterway in northern Canada. Some of its tributaries include the Liard River, Peel River, and Great Bear River. Its headwaters are in Great Slave Lake, and it flows northward through the Northwest Territories, receiving tributaries such as the Liard River, Peel River, and Great Bear River. The Mackenzie River eventually empties into the Beaufort Sea, an arm of the Arctic Ocean.