That's an easy one. The core philosophy in conservatism is maintaining the existing power structures in society. The size of government is immaterial, and will be increased when necessary and decreased when unnecessary to the achievement of this aim. The existing power structure in the USA is based around the military industrial complex, which dictates big, big, big government (but which spends very little on actual social programs). The power structure in Canada is based around the resource economy, which dictates government small enough that the energy, mining, and forestry companies can override popular opposition. That pretty much explains everything you need to know about the differences between American and Canadian conservatives.