Many of the things above that you list have variations that aren't too difficult and make good tours.

In northern Canada is a trip up the Dempster Highway to Inuvik:
http://www.mvermeulen.com/yukon.html

In the US is a trip up the Dalton Highway to Prudhoe Bay:
http://www.mvermeulen.com/dalton/index.html

The main roads across Siberia are a little more difficult but still do-able:
http://www.bikerussia.com/category/a...ussia/siberia/

Roads I haven't done that would be a bit more difficult than that but still do-able would be things like the Road of Bones in Russian Far east to Magadan or the Canol Road (particularly parts no longer maintained) in northern Canada. Doing any of these things in winter also puts them in a whole new dimension.

However, these are really still much easier than notions of setting across Antarctica or parts of the Arctic ice sheets. Also interestingly enough, despite the reputation of the name Siberia, I found the gaps between services and overall remoteness to be greater in Northern Western Australia than across Russia. Within Russia, there was a main trans-Siberian railroad lines which led to small towns and villages settled along the way. While the Russian Far east was only opened after fall of the Soviet Union and a gravel road constructed across the gaps in 1990s/2000s and officially opened in 2004 - it goes past many of these small villages.

I have a goal/dream to eventually cycle six continents (and have gone across four) but I don't foresee ever riding in Antarctica.