This work studies the effect of dry storage casks with different fuel loadings on the lowest upper limit of heat load (or heat load limit in short) of disposal canisters for a deep geological repository under the premise of minimizing the number of canisters used. An optimization procedure based on the simulated annealing algorithm is developed to generate the optimal loading configurations of canisters whose spent nuclear fuels (SNFs) are taken from a group of dry storage casks and find the heat load limit of canisters. Two BWR SNFs datasets are used in the analysis and the decay heat for each SNF is calculated via the second revision of the Regulatory Guide 3.54 methodology. Three kinds of fuel loading methods for dry storage casks are developed, and three loading scenarios of canisters are studied. The analysis results show that the heat load limit of canisters is affected by the annual disposal rate of canisters. As the annual disposal rate increases, the heat load limit also increases, and the effect of the fuel configuration of dry storage casks on the heat load limit of canisters decreases gradually. Casks_C3 and Casks_C4 with different D values is the best approach for finding the smallest heat load limit of canisters if multi-year disposal is used.