Critical loads of acidity (sulphur and nitrogen) for terrestrial (natural) ecosystems were determined for all provinces and territories of Canada. The approach used the Steady-State Mass Balance model with newly available high-resolution raster maps of soils and forest cover to estimate critical loads. The new high-resolution maps were used to estimate base cation weathering rate, define spatially-explicit base cation/aluminum ratios to protect selected plant species, and to estimate nutrient removal by forest harvesting. Critical loads were estimated under two ‘protection level’ scenarios: a 5% and 20% growth reduction to plant roots (specified through the base cation/aluminum ratio). In general, the lowest critical loads (<200 eq ha^–1 yr^–1) across both scenarios are found in northern Ontario, northern Manitoba, Labrador, mainland Nunavut and some regions of the arctic.  The 20% growth reduction scenario results in higher critical loads for much of the arctic, but the 5% growth reduction scenario reduces Nunavut to critical loads below 300 eq ha^–1 yr^–1.