Hey Ben,
The Canadian Glacier National Park (North West of the one in the USA) has 10m (10m Horizontal, 5m Vertical accuracy) data available. If you are downloading from the Canadian Server the sheets you want for basic coverage are (82N03, 82N04, 82N05 and 82N06) obviously if you wanted a larger area around the park, you would need additional sheets.
Just curious, but what is your process for converting the data for use as a TER? Do you use the default TER export options in Global Mapper, or do you customize the terrain spacing?