Depends on where they drop you off between excursions. To get from the ship to the Red Onion or the Sweet tooth, you have to walk into town (not far but probably at least 10 to 15 mins of walking. You need to be back at the ship to get on the White Pass train (that is where they board) so you are very limited on choices. I don't remember a whole lot of choices near the ship.
If you can get your first tour to drop you off in town at the Onion, then that might be doable...
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013