Knowledge of whether earthquake activity will increase in the next few thousand years is important for the planning of nuclear waste repositories. Assuming that fault instability portends earthquake activity, the rate of change in fault instability for the next few thousand years in eastern Canada is computed for two viscosity models. It is shown that a uniform-viscosity (1 x 1021 Pa ·s) mantle predicts decreasing fault instability. However, a high-viscosity (1 x 1023 Pa ·s) lower mantle predicts a significant increase in fault instability, with an overall rate of -0.06 MPa/ka. Due to the lack of consensus on lower mantle viscosity, the case for increasing earthquake activity is definitely a possibility, so more study on mantle rheology, ice deglaciation history, and intraplate earthquakes in the planning of nuclear waste repositories is needed.