Our Verizon phone worked almost everywhere in AK. We lost service on the Denali and Cassair Highways but just about everywhere else it worked. We had text service the entire route from TX to Prudhoe Bay and back. They were installing fiber optic cable along the haulroad between Fairbanks and Prudhoe in 2014. Some portions have washed out with the flooding this spring.
We did not get a Canada plan. Just told everyone to text us while we were in Canada.
Mi-Fi is very spotty and usually weak all along the Alaska Highway and throughout AK. We could usually hook up enough to check email but that was about it.
In talking to people along the way we came the conclusion that Verizon is the most reliable.