Amsoil signature series 0w-30... hands down the best cold starting viscosity. Your engine will start without a block heater in below -40 C temps, guaranteed. In Canada, Amsoil is less expensive (relatively) than other oils compared to buying in the USA. I can buy a gallon of Amsoil Signature for $37 versus $40+ for Pennzoil.
I live in Saskatchewan and we regularly are around -20C in winter with cold snaps of -30C (-22F) and even occasionally down to -40C nearly (-40 F). You better have a healthy battery at these temps, along with battery warmer OR a trickle charger, not both.
Personally, I would use Amsoil 0w-30 along with an oil pan heater for those super cold days.