Extreme Cold and Icing Conditions Testing
You probably need to consider two separate locations.
Northern Canada has the ‘cold’ and probably reasonable snow for the ground handling aspects.
However for in-flight icing tests you need water and warmer conditions. The Southern Alps and Switzerland has been suggested, but this may be complicated by civil traffic. Alternatively Iceland / Greenland could be considered, but may lack facilities or offer reasonable continuity of weather conditions.
IIRC Boeing uses the West coast of Canada which may have advantages of a range of airports (Seattle to Alaska) and transit to other parts of N America as conditions change.
You look for some active CB's at FL200, and you get into them, right?
Not necessarily so !
Good conditions for certification icing are often found in stratoform clouds and these would satisfy the ‘continuous’ icing aspects. The ‘high rate’ requirements are related to Cbs, but testing in Cbs is not advisable due to the ‘unknown’ and variability of such clouds.
The rules have changed since I flew icing tests, so the mix of ice shape and real ice flying may be different, but it was possible to complete a full programme in layered clouds given their availability and a range of temperature / water content, together with a range of ice 'shape' flying.