When Jack is trapped in the gold mine, Alex's lamp is not lit as he runs to help. However in the next shot it is.
When White Fang is fighting Cherokee, he appears to be wearing a chain collar that disappears as they fight.
During the bear chase and fight, an apple is seen being thrown from off-camera (to get the bear to turn around).
While Jack is re-taming White Fang, countless ATV tire tracks are seen underfoot, smoothing out the river sand, near his Dad's gold claim.
The map at the beginning of the movie shows Juneau north of Skagway. In reality, Juneau is over a hundred miles south of Skagway.
The trees in the movie are large and robust. Yukon, and especially Klondike, trees are stunted by the harsh climate.