I can comment a bit for the route in Canada, I highly suggest taking the Cassiar Highway (#37), then you can either go to Prince Rupert and ferry to Port Hardy or Vancouver or go to Prince George and pick a route going south from there.
The Cassiar has no services but you can get some wi-fi if you stay at the lodges on the way (I didn't). The scenery is amazing and definitely worth it!
In terms of services/grocery stores, from Whitehorse:
~200km Teslin (small store, not too much variety but it has good prices. Stock up for the Cassiar here unless you are making 20km detour to Watson lake)
~400km after teslin, is Dease Lake (good store - u can find fruit)
~83km to Iskut (has store)
~150km to Bell 2 lodge (has store)
~100km to Meziadin junction (if u take detour, there are lots of services in Stewart/Hayder), if you dont detour, the campground has a small store - with surprisingly low prices but not big selection
From there (200km) there's not much until New Hazelton (Kitwanga and another small village before it have a store)

well if you decide to do this route and have more questions, PM me

You will probably meet other cyclists too, I met about 10 people who had taken that route when I was heading north.