Climate variability, cultivar, and sowing date are some of the factors affecting the yield and productivity of a given crop. Evaluating the effect of all these factors, and their combination, through field experimentation is not always feasible. However, validated crop models are efficient and economically effective tools to analyse the influence these factors have on crop yield and production.The APSIM program is one of such models which are widely used to simulate crop yield and resource use under different scenarios. In this study, the APSIM-CANOLA module, with long-term climate records, was used to examine the effects of seasonal variability, sowing date and plant available water at sowing on grain yield of several canola cultivars. There was high year to year variability of simulated crop yield in response to the amount of rain. Water use efficiency was found to be cultivar dependent.Sowing date affects the length of crop growing season and hence crop yield. Higher starting soil water significantly contributes to crop production. Break-even canola grain yields were attainable with high probability but higher yields were increasingly less probable and unattainable with some cultivars and under certain sowing and rainfall conditions.