In the US, the most standard "fixed rate" mortgage has the rate fixed for 30 years. A mortgage where the rate changes before loan maturity would be called an "adjustable rate mortgage" ("arm" for short).
Aren't we only talking about a difference in term length then? i.e. it's more common for the term length to equal the amortization length in the U.S.? In Canada even the amortization/maturity can't be greater than 25 years. And terms are commonly 5 years.