Sirius is currently approaching the solar system, at a rate of 5.5 km/s, consequently in the future it will be closer and therefore brighter. When will Sirius pass closest to the solar system? How far will it then be from the sun, and what magnitude will it reach?
Sirius is moving towards the sun at 5.5 km/s, and according to Sky and Telescope, will reach its closest distance in 60000 years, at which time it will be 7.8 light years distant, and be at magnitude -1.64, only slightly brighter than it's current magnitude -1.46.
Calculations using the latest Hippacos results give a slightly different value: a closest approach of 8.18 ly in 46000 years, and consequently a slightly dimmer peak. However Sirius is not moving rapidly relative to the sun, and will not change its brightness greatly in the next 100000 years or so
It will be the brightest star in the sky for another 90000 years, and no star will match its current brightness for another million years (when delta Scuti will reach magnitude -1.84.