We explore sets of measures by which Canada could achieve CO2 emission reductions of 50% or 75%. Full implementation of cost-effective efficiency measures, combined with substantial fuel switching from coal and oil to natural gas (NG), will only slightly reduce Canadian CO2 emissions in 2020 compared to 1991, given the high growth in energy-intensive industries assumed in the reference scenario. To achieve a 50% emission reduction requires more fundamental changes involving, for example, constant economic output from energy-intensive industries (with compensating increases elsewhere in the economy), limiting the increase in rotal distance travelled by light vehicles, displacement of 30-80% (depending on the region) of the remaining fossil-fuel-generated electricity with electricity derived from renewable energy, and use of hydrogen (H-2) derived from renewable energy in selected niche markets. The 75% emission-reduction target will require greater use of H-2, but replacement of direct use of NG in commercial and residential buildings with H-2 would not be required if other measures are implemented to the extent assumed here.