"if Saskatchewan doesn't implement a price on carbon, does that undermine other provinces' efforts to reduce GHGs or Ottawa's chances of meeting its international targets? The answer is yes, which suggests it is a matter of national concern." 
The answer is no. 
1) A carbon tax has very limited influence on fuel consumption. 
2) Saskatchewan sequesters large amounts of carbon which helps meet targets. 
3) Saskatchewan also has other CO2 reduction programs and initiatives that are more suited to its situation.