Gulf of St. Lawrence doesn't have a single longitude and latitude as it's a large body of water.

It's more accurate to provide coordinates for specific locations within the Gulf:

* Approximate center of the Gulf: 47.5° N, 62.0° W

* Mouth of the Gulf, where it opens into the Atlantic: 47.0° N, 59.0° W

Here are some key points within the Gulf with their coordinates:

* Prince Edward Island: 46.5° N, 63.0° W (approximate)

* Cape Breton Island: 46.0° N, 60.0° W (approximate)

* Anticosti Island: 49.0° N, 63.0° W (approximate)

Keep in mind these are approximate coordinates. For more precise locations, you can use online mapping tools.