We are UK citizens driving from Patagonia to Alaska, then shipping home from New York. We hope to be in the US for 3 months, a couple of months in Canada then into Alaska for a couple of months and then back into Canada and the US. But cannot find information about whether we can get a new visa waiver in Canada for driving to Alaska and then back into the US?
This is how I understand this works:
After you arrived in the US, you have 90 days to stay before you have to leave. If within the 90 days you go into Mexico or Canada and want to come back to the US (which by going to Alaska is something you plan to do) you don't reset your 90 days. In other words you have to finish the whole trip from the Mexico border up to Alaska and over to New York in the first 90 days (which you don't want to do).
If you hand in your I94 when leaving the US for Canada, there is no guarantee that they'll give you a new one when you arrive in Alaska, because you just used up your 90 days a few weeks before.
This is basically to prevent 'visa-runs' into Mexico or Canada.
You need a third 'new entry' when coming back from Canada into the US.
While it is perfectly possible that the border officials issue a new I94 in both cases, this is by no means certain.
I would further investigate this and maybe just get a multiple-entry visa to be on the safe side.
Check out some official information about the visa waiver program.