Alaska is a US state and shouldn't require a separate visa

to return to the lower 48 states.

The only potential exceptions would be:
1. You flight has a connection in Canada.
2. You flight does not have a scheduled stop in Canada but makes an unexpected landing in Canada, due to weather or mechanical problem or any unforseeable events - this is rare but possible.
3. You are flying to Alaska for a cruise that has port of calls in Canada.
4. You drive into Canada from Alaska, which some people do. As an example, cruise passengers often drive into to Canada from Skagway.