Let's be accurate. To the best of my knowledge the curse was upon Canaan, who was one of the sons of "Ham", not on all of the sons of "Ham". Unless you can show me a source that states otherwise.
Even if one is a Canaanite, under certain circumstances, they have the option to convert [for example, before the war starts for the conquest of the land of Israel].
Rahab [see the book of Yehoshua/Joshua chapter 2] was from the descendants of Canaan, but converted to Judaism and married the prophet Yehoshua [tractate Megilla 14b].
A separate question is, did the ethiopian "Jews" make their way into the Jewish nation by a valid conversion.
This is a point of debate among Rabbis of today, some say yes, some say no and others say we have a doubt.