I broke down half way between Fort Nelson, BC and Fort St. John, BC. a few years ago. It is a long way from nowhere. I was blessed in a trucker stopped and he climbed to the top of a earth mover he was transporting and got cell service. A tow truck came out of Fort St. John and they towed me. I had to pay the tow bill which was $650, but my insurance paid it within 3 days of me mailing it to them. Everything worked great.
Now on cell service you really want to check. I usually pick up a trac phone in the first town I hit in Canada and then turn my phone off. Data prices can be quite expensive and only if you have an international plan do the rates for phone calls come down. Cell service is very spotty. I just did the Cassier both ways and there was no cell phone service on it. If you get around a bigger town you can get it. I live in Haines, Ak.