Wow that is a lot of mileage on a bike not sure how you guys manage, I feel like a bit of a wimp, on that trip north then across Midwest to Tennesee up to Ontario, my best days were around 300 miles and I thought I was doing good. Even worst in 2002 we rented a scooter in Italy for six weeks and the best we did there was 70 a day., and that was kms..... too many distractions, it was harvest time so there seemed to be a festival in every town and a town around every corner.
Last summer we did the Trans Labrador which is touted as the new Alaska highway, we drove just about everyday covered 7700 kms in six weeks, not so many distractions, 1000kms of gravel mixed in between rough and new paved sections, up to 425kms between services stations and nothing in between except wilderness. I still prefer the Alaska highway, but definatly an interesting journey and worth a look. consider an extra spare, I guess it would be similar on the Alaska if you plan on driving fast, I didn't have one but I never went over 55 mph ,most of the time a lot slower and had 10 ply tires, However I did bring 30 litres of extra fuel but never needed it. Fuel gets more expensive the further Norht you go and when you are the only show in town you can charge what you like so extra fuel is not a crazy idea even if you can do the distances. A lot of people with flat tires, most were driving over 60mph. We met 4 over a period of one and a half days one had two flats on a section that had over 400kms between services.
Last time I went up in 2008 I noticed a lot of service stations closed down.