Cut halibut into pieces, about 3 inches square. Pieces should be no more than an inch thick; slice in half horizontally if necessary. Pat dry. In a small bowl, beat egg whites until stiff. Set aside.
In medium mixing bowl, combine flour, salt, and oil. Pour in beer and whisk until just smooth. Fold in egg whites.
Heat about 1/2 inch of canola oil in a large saute pan, then reduce heat to medium-low. Dip each piece of fish into the batter and fry for about 8-12 minutes per side, depending on size and thickness. As each piece comes out of the oil, drain on paper towels. Serve immediately, with tartar sauce.