The definition of magnetic north is the point on the earth's surface at which a compass needle would point straight down (if you can get there this will actually happen). Magnetic north's position is periodically updated (which requires people on the ground, and a number of measurements over time to average out short term anomalies) to re-calculate magnetic declination.
The magnetic North Pole is not (usually) in the same place like the true North Pole is: it moves. Over the past century it has moved over 900 kilometres - and the rate of movement is increasing - between 1984 and 1994 it moved an astonishing 150 kilometres. Short-term jumps of as much at 80 kilometres in one day have been recorded. The movement is caused by irregularities in the currents of iron-containing magma that flows far below the earth's surface.
At this rate magnetic north will soon be outside of Canadian territory (depending on your definition, see Canadian Arctic Sovereignty). The last results I have (from the Januray/Feburary 1995 edition of Canadian Geographic magazine) put it under the western side of Ellef Ringnes Island - 1300 kilometres south of the true North Pole. If it continues moving in its current north by northwest direction it will soon clear the last of the Arctic Archipelago. | 
