My 1st trip up the Alcan....'72 or '74 can't recall...it seemed like $1500 was a good amount...or that was all that I had to my name at the time, not sure. In any case, that always worked for the next 25 years and circa 20 trips. Never found a place that wouldn't take either Visa or MC in Canada since circa early 80's, but I never ventured too far off the Alcan and wasn't RV'ng, so maybe one needs the right amount of cash even now.
I'd second Joe's suggestion: If you're out in Bush Alaska...even on the remote parts of the road system that pretend to be Bush Alaska, take some cash. Even in recent years, when I fly around SC Alaska, I always carry at least $1000 in cash "just because".....